ath79: Refactor GL.iNet GL-AR300M-series generic.mk

Rework DEVICE_VENDOR, DEVICE_MODEL, and DEVICE_VARIANT
for the GL-AR300M series on the ath79-generic target.

Changes GL-AR300M-Lite to the current form with
DEVICE_VARIANT := Lite (board name is unchanged)

Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>

target/linux/ath79/image/generic.mk

@@ -549,6 +549,7 @@ TARGET_DEVICES += glinet_gl-ar150
 
 define Device/glinet_gl-ar300m-common-nor
   ATH_SOC := qca9531
+  DEVICE_VENDOR := GL.iNet
   DEVICE_PACKAGES := kmod-usb2
   IMAGE_SIZE := 16000k
   SUPPORTED_DEVICES += gl-ar300m
@@ -556,14 +557,13 @@ endef
 
 define Device/glinet_gl-ar300m-lite
   $(Device/glinet_gl-ar300m-common-nor)
-  DEVICE_VENDOR := GL.iNet
-  DEVICE_MODEL := GL-AR300M-Lite
+  DEVICE_MODEL := GL-AR300M
+  DEVICE_VARIANT := Lite
 endef
 TARGET_DEVICES += glinet_gl-ar300m-lite
 
 define Device/glinet_gl-ar300m-nor
   $(Device/glinet_gl-ar300m-common-nor)
-  DEVICE_VENDOR := GL.iNet
   DEVICE_MODEL := GL-AR300M
 endef
 TARGET_DEVICES += glinet_gl-ar300m-nor