meson: switch code dependency to libsystemd

For a while now systemd has packaged a separate `libsystemd`.  For
meson dependency, `systemd` should be used when looking for systemd
service file paths and `libsystemd` should be used for `sd_*` functions.

Update the dependency accordingly.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I606d1dee9ac96025f3a1059fbfbba9bc6f8b27f0
diff --git a/meson.build b/meson.build
index f5a1d74..b9f88ed 100644
--- a/meson.build
+++ b/meson.build
@@ -30,7 +30,7 @@
         dependency('phosphor-dbus-interfaces'),
         dependency('phosphor-logging'),
         dependency('sdbusplus'),
-        dependency('systemd'),
+        dependency('libsystemd'),
 ]
 
 if(get_option('usb-code-update').allowed())