ramips: clean UBI tempdir before image creation

Clean the temporary directory the UBI image is generated from before
generation.

Currently it is removed after the image generation, which leads to files
possibly not being cleared after a build failure in this step.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ramips/image/mt7621.mk

@@ -92,6 +92,7 @@ define Build/inteno-y3-header
 endef
 
 define Build/inteno-bootfs
+	rm -rf $@.ubifs-dir
 	mkdir -p $@.ubifs-dir/boot
 
 	# populate the boot fs with the dtb and the kernel image
@@ -100,7 +101,6 @@ define Build/inteno-bootfs
 
 	# create ubifs
 	$(STAGING_DIR_HOST)/bin/mkfs.ubifs ${MKUBIFS_OPTS} -r $@.ubifs-dir/ -o $@.new
-	rm -rf $@.ubifs-dir
 	mv $@.new $@
 endef