Fix backlight on some Samsung devices

Some Samsung Q vendor devices have HWC rather than lights hal control.
In those cases, backlight is controlled through another SELinux context.
We used to correct this SELinux context for all devices, however this is
no longer needed, and actually breaks those devices.

So, change SELinux context, only if uid/gid is wrong

rw-system.sh

@@ -816,9 +816,11 @@ fi
 
 if getprop ro.vendor.build.fingerprint |grep -qiE '^samsung/';then
     for f in /sys/class/lcd/panel/actual_mask_brightness /sys/class/lcd/panel/mask_brightness /sys/class/lcd/panel/device/backlight/panel/brightness /sys/class/backlight/panel0-backlight/brightness;do
-        chcon u:object_r:sysfs_lcd_writable:s0 $f
-        chmod 0644 $f
-        chown system:system $f
+        if [ "$(stat -c '%U' "$f")" == "root" ];then
+            chcon u:object_r:sysfs_lcd_writable:s0 $f
+            chmod 0644 $f
+            chown system:system $f
+        fi
     done
 
     setprop persist.sys.phh.fod.samsung true