image: fix ar71xx legacy images

If TARGET_PER_DEVICE_ROOTFS and DEVICE_PACKAGES are used for ar71xx
legacy images:

- an already jffs2 padded squashfs rootfs is overwritten
  with an unpadded/raw one.

- the squashfs-raw and squashfs-64k rootfs are not replaced by the
  ones including the DEVICE_PACKAGES

Call Image/Build/squashfs after the DEVICE_PACKAGES are added to the
base squashfs rootfs to fix the issues.

Fixes: FS#904

Signed-off-by: Mathias Kresin <dev@kresin.me>

include/image-legacy.mk

@@ -48,6 +48,7 @@ endef
 ifdef TARGET_PER_DEVICE_ROOTFS
   define Image/Build/Profile/Filesystem
 	cp $(KDIR)/root.$(2)+pkg=$(3) $(KDIR)/root.$(2)
+	$(call Image/Build/$(2),$(2))
 	$(call Image/Build/Profile,$(1),$(2))
   endef
 else