Backend: ensure we've got a POSIX accepting chown via our busybox

- per https://github.com/osm0sis/AnyKernel2/pull/10#issuecomment-283771783

META-INF/com/google/android/update-binary

@@ -16,7 +16,7 @@ show_progress() { echo "progress $1 $2" > $OUTFD; }
 set_perm_recursive() {
   dirs=$(echo $* | $bb awk '{ print substr($0, index($0,$5)) }');
   for i in $dirs; do
-    chown -R $1:$2 $i;
+    $bb chown -R $1:$2 $i;
     find "$i" -type d -exec chmod $3 {} +;
     find "$i" -type f -exec chmod $4 {} +;
   done;