ar71xx: fix sysupgrade for Arduino Yun

Commit bb46b63 changed its partition scheme, but sysupgrade image
validation still uses the old format. This commit fixes it so that
force flag is not needed for sysupgrade.

Fixes: bb46b63 ("ar71xx: move Arduino Yun to generic building code")
Signed-off-by: Sungbo Eo <mans0n@gorani.run>

target/linux/ar71xx/base-files/lib/upgrade/platform.sh

@@ -217,6 +217,7 @@ platform_check_image() {
 	archer-c60-v2|\
 	archer-c7-v4|\
 	archer-c7-v5|\
+	arduino-yun|\
 	bullet-m|\
 	bullet-m-xw|\
 	c-55|\
@@ -346,7 +347,6 @@ platform_check_image() {
 	ap152|\
 	ap91-5g|\
 	ap96|\
-	arduino-yun|\
 	bhr-4grv2|\
 	bxu2000n-2-a1|\
 	db120|\