ipq40xx: fix image pipeline for MR6350

Add two missing $$ in the factory image build pipeline for MR6350

Signed-off-by: Zeyu Dong <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/21682
Signed-off-by: Robert Marko <[email protected]>
(cherry picked from commit 979f70cc7ec6cec28d9f3d1ec6a4ef54fd265dc2)

target/linux/ipq40xx/image/generic.mk

@@ -726,7 +726,7 @@ define Device/linksys_mr6350
 	PAGESIZE := 2048
 	UBINIZE_OPTS := -E 5    # EOD marks to "hide" factory sig at EOF
 	IMAGES += factory.bin
-	IMAGE/factory.bin  := append-kernel | pad-to $$(KERNEL_SIZE) | append-ubi | linksys-image type=MR6350
+	IMAGE/factory.bin  := append-kernel | pad-to $$$$(KERNEL_SIZE) | append-ubi | linksys-image type=MR6350
 	DEVICE_PACKAGES := ipq-wifi-linksys_mr6350 kmod-usb-ledtrig-usbport
 endef
 TARGET_DEVICES += linksys_mr6350