ar71xx: fix MikroTik rb-nor-flash-16M-ac image

commit e15c63a375
ar71xx: add support for MikroTik RouterBOARD wAP G-5HacT2HnD (wAP AC)

changed the existing rb-nor-flash-16M-ac image in a way that it would
now only support the rb-wapg-5hact2hnd.
The board show however rather be added to the existing boards in the
rb-nor-flash-16M image template.

Reported-by: Mathias Kresin <dev@kresin.me>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/ar71xx/image/mikrotik.mk

@@ -50,6 +50,6 @@ define Device/rb-nor-flash-16M-ac
   $(Device/rb-nor-flash-16M)
   DEVICE_TITLE := MikroTik RouterBoard (16 MB SPI NOR, 802.11ac)
   DEVICE_PACKAGES += kmod-ath10k ath10k-firmware-qca988x ath10k-firmware-qca9887
-  SUPPORTED_DEVICES := rb-wapg-5hact2hnd
+  SUPPORTED_DEVICES += rb-wapg-5hact2hnd
 endef
 TARGET_DEVICES += rb-nor-flash-16M-ac