ar71xx: image: rework EnGenius ENS202EXT factory image

Current EnGenius ENS202EXT factory image recipe version causes factory
images of the following devices to be corrupted. This issue wasn't
visible until recent changes of image Makefile snippets order.

Signed-off-by: Mathias Kresin <dev@kresin.me>
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>

target/linux/ar71xx/image/generic-senao.mk

@@ -1,12 +1,9 @@
 define Build/senao-factory-image
-	$(eval board=$(word 1,$(1)))
-	$(eval rootfs=$(word 2,$(1)))
-
 	mkdir -p $@.senao
 
-	touch $@.senao/FWINFO-OpenWrt-$(REVISION)-$(board)
-	$(CP) $(IMAGE_KERNEL) $@.senao/openwrt-senao-$(board)-uImage-lzma.bin
-	$(CP) $(rootfs) $@.senao/openwrt-senao-$(board)-root.squashfs
+	touch $@.senao/FWINFO-OpenWrt-$(REVISION)-$(1)
+	$(CP) $(IMAGE_KERNEL) $@.senao/openwrt-senao-$(1)-uImage-lzma.bin
+	$(CP) $@ $@.senao/openwrt-senao-$(1)-root.squashfs
 
 	$(TAR) -c \
 		--numeric-owner --owner=0 --group=0 --sort=name \
@@ -25,7 +22,7 @@ define Device/ens202ext
   IMAGE_SIZE := 13632k
   IMAGES += factory.bin
   MTDPARTS := spi0.0:256k(u-boot)ro,64k(u-boot-env),320k(custom)ro,1536k(kernel),12096k(rootfs),2048k(failsafe)ro,64k(art)ro,13632k@0xa0000(firmware)
-  IMAGE/factory.bin/squashfs := append-rootfs | pad-rootfs | senao-factory-image ens202ext $$$$@
+  IMAGE/factory.bin := append-rootfs | pad-rootfs | senao-factory-image ens202ext
   IMAGE/sysupgrade.bin := append-kernel | pad-to $$$$(KERNEL_SIZE) | append-rootfs | pad-rootfs | check-size $$$$(IMAGE_SIZE)
 endef
 TARGET_DEVICES += ens202ext