ramips: fix broken UniFi 6 Lite image

Ubiquiti's own bootloader expects the configuration mode to be present
with a "@" instead of a "-" for the sperator character. Otherwise
booting of the image fails.

Signed-off-by: David Bauer <[email protected]>

target/linux/ramips/image/mt7621.mk

@@ -1193,6 +1193,7 @@ define Device/ubnt_unifi-6-lite
   $(Device/dsa-migration)
   DEVICE_VENDOR := Ubiquiti
   DEVICE_MODEL := UniFi 6 Lite
+  DEVICE_DTS_CONFIG := config@1
   DEVICE_PACKAGES += kmod-mt7603 kmod-mt7915e
   KERNEL := kernel-bin | lzma | fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
   IMAGE_SIZE := 15424k