build: make sure that $(STAGING_DIR_IMAGE) exists

Call 'mkdir -p $(STAGING_DIR_IMAGE)' before trying to store files in
this potentially non-existing folder.

Signed-off-by: Daniel Golle <[email protected]>

include/image-commands.mk

@@ -53,6 +53,7 @@ define Build/append-image-stage
 	cp "$(BIN_DIR)/$(DEVICE_IMG_PREFIX)-$(1)" "[email protected]"
 	fwtool -s /dev/null -t "[email protected]" || :
 	fwtool -i /dev/null -t "[email protected]" || :
+	mkdir -p "$(STAGING_DIR_IMAGE)"
 	dd if="[email protected]" of="$(STAGING_DIR_IMAGE)/$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))-$(DEVICE_NAME)-$(1)"
 	dd if="[email protected]" >> "$@"
 	rm "[email protected]"