mboxd: Use escaped unit names for device dependencies

Inspecting the journal showed that the device units that mboxd depends
on were timing out:

    Jan 30 02:48:29 witherspoon systemd[1]: Timed out waiting for device dev-aspeed-lpc-ctrl.device.
    Jan 30 02:48:29 witherspoon systemd[1]: dev-aspeed-lpc-ctrl.device: Job dev-aspeed-lpc-ctrl.device/start failed with result 'timeout'.
    Jan 30 02:48:29 witherspoon systemd[1]: dev-aspeed-mbox.device: Job dev-aspeed-mbox.device/start timed out.
    Jan 30 02:48:29 witherspoon systemd[1]: Timed out waiting for device dev-aspeed-mbox.device.
    Jan 30 02:48:29 witherspoon systemd[1]: dev-aspeed-mbox.device: Job dev-aspeed-mbox.device/start failed with result 'timeout'

As it turns out, systemd wants escaped strings to cope with e.g. paths
with dashes in the filename. Update the Wants/After lines to use the
escaped strings. The escaped values were created running
`systemd-escape`[1] on a Zaius image under QEMU:

    root@zaius:~# systemd-escape -p /dev/aspeed-*
    dev-aspeed\x2dlpc\x2dctrl dev-aspeed\x2dmbox

This leaves us with the happy result of no timeouts:

    # journalctl | grep aspeed
    ...
    Feb 06 02:25:22 zaius systemd[1]: Found device /dev/aspeed-mbox.
    Feb 06 02:25:25 zaius systemd[1]: Found device /dev/aspeed-lpc-ctrl.
    ...

[1] https://www.freedesktop.org/software/systemd/man/systemd-escape.html#

Change-Id: I4770026842757768b20b919125af47ae499d1667
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/common/recipes-phosphor/mboxd/mboxd/mboxd.service b/common/recipes-phosphor/mboxd/mboxd/mboxd.service
index ad3d145..0d37a48 100644
--- a/common/recipes-phosphor/mboxd/mboxd/mboxd.service
+++ b/common/recipes-phosphor/mboxd/mboxd/mboxd.service
@@ -1,9 +1,10 @@
 [Unit]
 Description=Phosphor MBOX Daemon
-Wants=dev-aspeed-mbox.device
-After=dev-aspeed-mbox.device
-Wants=dev-aspeed-lpc-ctrl.device
-After=dev-aspeed-lpc-ctrl.device
+Wants=dev-aspeed\x2dlpc\x2dctrl.device
+After=dev-aspeed\x2dlpc\x2dctrl.device
+Wants=dev-aspeed\x2dmbox.device
+After=dev-aspeed\x2dmbox.device
+
 
 [Service]
 Restart=always