addonsu: Don't mount SAR system to /system

Change-Id: Ic2f0a994477a5bc04b32e24b0bd4baaa2773ff55
diff --git a/addonsu/unmount-system.sh b/addonsu/unmount-system.sh
index 60c5e18..19b3431 100644
--- a/addonsu/unmount-system.sh
+++ b/addonsu/unmount-system.sh
@@ -3,13 +3,13 @@
 # Modern devices use /system as root ("/")
 system_as_root=`getprop ro.build.system_root_image`
 if [ "$system_as_root" == "true" ]; then
-  if umount /system && umount /system_root; then
+  if umount /system_root; then
     exit 0
   fi
-fi
-
-if umount /system; then
+else
+  if umount /system; then
     exit 0
+  fi
 fi
 
 exit 1