flo: rootdir: Change user/group permission for charger

Make charger binary run as system instead of root. Since it
needs to handle input key events, add input as a supplemental
group in addition to system and graphics.

Change-Id: Id1dc46f335087147b7d8cf674664c26f0b511de1

rootdir/etc/init.flo.rc

@@ -320,6 +320,8 @@ on property:ro.data.large_tcp_window_size=true
 
 service charger /charger
     class charger
+    user system
+    group system graphics input
     critical
     seclabel u:r:charger:s0