pistachio: Fix FIT image configuration name

The pistachio U-Boot expects a default configuration with the name
config@1 in the FIT image. The default was changed in OpenWrt some
months ago.
This makes the board boot again.

Fixes: 9f714398e060 ("build: use config-1 instead of config@1 as default")
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/pistachio/image/Makefile

@@ -15,6 +15,7 @@ define Device/Default
   KERNEL_SUFFIX := -kernel.itb
   KERNEL_INSTALL := 1
   KERNEL_IN_UBI := 1
+  DEVICE_DTS_CONFIG := config@1
   IMAGES := factory.ubi sysupgrade.tar
   IMAGE/factory.ubi := append-ubi
   IMAGE/sysupgrade.tar := sysupgrade-tar