ramips: add image checks

As long as we can't enforce image metadata, we need to use (platform)
image checks to have at least soem kind of validation.

Signed-off-by: Chen Minqiang <ptpt52@gmail.com>

target/linux/ramips/base-files/lib/upgrade/platform.sh

@@ -264,9 +264,11 @@ platform_check_image() {
 		;;
 	hc5962|\
 	mir3g|\
-	r6220)
-		# these boards use metadata images
-		return 0
+	r6220|\
+	ubnt-erx|\
+	ubnt-erx-sfp)
+		nand_do_platform_check "$board" "$1"
+		return $?;
 		;;
 	re350-v1)
 		[ "$magic" != "01000000" ] && {
@@ -275,11 +277,6 @@ platform_check_image() {
 		}
 		return 0
 		;;
-	ubnt-erx|\
-	ubnt-erx-sfp)
-		nand_do_platform_check "$board" "$1"
-		return $?;
-		;;
 	wcr-1166ds|\
 	wsr-1166)
 		[ "$magic" != "48445230" ] && {