ramips: fix sysupgrade image for TP-Link RE200v1

Images generated for the TP-Link RE200v1 cannot be updated using
sysupgrade, because a necessary call to append-metadata was missing.

Signed-off-by: Andreas Böhler <dev@aboehler.at>

target/linux/ramips/image/mt7620.mk

@@ -962,7 +962,7 @@ define Device/tplink_re200-v1
   DEVICE_VARIANT := v1
   DEVICE_PACKAGES := kmod-mt76x0e
   IMAGES += factory.bin
-  IMAGE/sysupgrade.bin := mktplinkfw sysupgrade -e -O
+  IMAGE/sysupgrade.bin := mktplinkfw sysupgrade -e -O | append-metadata
   IMAGE/factory.bin := mktplinkfw factory -e -O
   IMAGE_SIZE := 7936k
   KERNEL := $(KERNEL_DTB)