use busctl set-property in led group start/stop services

This change replaces `busctl call` with `busctl set-property`
in LED group start and stop service units, aligning with its
intended use.

Tested:

Loaded the image with the changes into qemu:

```
root@bmc:~# busctl get-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/fan0_ok xyz.openbmc_project.Led.Group Asserted
b true
root@bmc:~# systemctl status obmc-led-group-start@fan0_ok.service
* obmc-led-group-start@fan0_ok.service - Assert fan0_ok LED
     Loaded: loaded (/usr/lib/systemd/system/obmc-led-group-start@.service; static)
     Active: active (exited) since Thu 2025-08-07 08:27:53 PDT; 47min ago
 Invocation: 3f0768ed25bb4056806304548f2e6759
    Process: 1306 ExecStart=/bin/sh -c busctl set-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/fan0_ok xyz.openbmc_project.Led.Group Asserted b true (code=exited, status=0/SUCCESS)
   Main PID: 1306 (code=exited, status=0/SUCCESS)
   Mem peak: 804K
        CPU: 444ms
Aug 07 08:27:51 bmc systemd[1]: Starting Assert fan0_ok LED...
Aug 07 08:27:53 bmc systemd[1]: Finished Assert fan0_ok LED.
root@bmc:~# systemctl stop obmc-led-group-start@fan0_ok.service
root@bmc:~# busctl get-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/fan0_ok xyz.openbmc_project.Led.Group Asserted
b true
root@bmc:~# systemctl status obmc-led-group-start@fan0_ok.service
* obmc-led-group-start@fan0_ok.service - Assert fan0_ok LED
     Loaded: loaded (/usr/lib/systemd/system/obmc-led-group-start@.service; static)
     Active: inactive (dead)
Aug 07 08:27:51 bmc systemd[1]: Starting Assert fan0_ok LED...
Aug 07 08:27:53 bmc systemd[1]: Finished Assert fan0_ok LED.
Aug 07 09:15:16 bmc systemd[1]: obmc-led-group-start@fan0_ok.service: Deactivated successfully.
Aug 07 09:15:16 bmc systemd[1]: Stopped Assert fan0_ok LED.
root@bmc:~# systemctl start obmc-led-group-stop@fan0_ok.service
root@bmc:~# busctl get-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/fan0_ok xyz.openbmc_project.Led.Group Asserted
b false
```

This shows that the property was successfully modified
via D-Bus using set-property.

Change-Id: I0033c892a3c227aa3c14a013f162f1b00f5ee542
Signed-off-by: William de Abreu Pinho <williamdapinho@gmail.com>
diff --git a/service_files/obmc-led-group-start@.service b/service_files/obmc-led-group-start@.service
index 30ddbfd..db8c6c3 100644
--- a/service_files/obmc-led-group-start@.service
+++ b/service_files/obmc-led-group-start@.service
@@ -8,5 +8,5 @@
 Type=oneshot
 RemainAfterExit=yes
 Restart=no
-ExecStart=/bin/sh -c "busctl call xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/%i org.freedesktop.DBus.Properties Set ssv xyz.openbmc_project.Led.Group Asserted b true"
+ExecStart=/bin/sh -c "busctl set-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/%i xyz.openbmc_project.Led.Group Asserted b true"
 SyslogIdentifier=obmc-led-group-start
diff --git a/service_files/obmc-led-group-stop@.service b/service_files/obmc-led-group-stop@.service
index 7608e50..c0312cf 100644
--- a/service_files/obmc-led-group-stop@.service
+++ b/service_files/obmc-led-group-stop@.service
@@ -8,5 +8,5 @@
 Type=oneshot
 RemainAfterExit=yes
 Restart=no
-ExecStart=/bin/sh -c "busctl call xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/%i org.freedesktop.DBus.Properties Set ssv xyz.openbmc_project.Led.Group Asserted b false"
+ExecStart=/bin/sh -c "busctl set-property xyz.openbmc_project.LED.GroupManager /xyz/openbmc_project/led/groups/%i xyz.openbmc_project.Led.Group Asserted b false"
 SyslogIdentifier=obmc-led-group-stop