ath79: enable forceless sysupgrade from ar71xx on fritz300e

This adds the ar71xx board name to the SUPPORTED_DEVICES on ath79,
so forceless sysupgrade on this device becomes possible.

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/ath79/image/generic.mk

@@ -158,6 +158,7 @@ define Device/avm_fritz300e
 	append-squashfs-fakeroot-be | pad-to 256 | append-rootfs | pad-rootfs | \
 	append-metadata | check-size $$$$(IMAGE_SIZE)
   DEVICE_PACKAGES := fritz-tffs rssileds -swconfig
+  SUPPORTED_DEVICES += fritz300e
 endef
 TARGET_DEVICES += avm_fritz300e