tools/mkimage: use full defconfig name

The defconfig file used to build tools is "tools-only_defconfig".
Though u-boot scripts can still automatically handle the old style
name for compatibility reason, it's better to use the correct name.

Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: openwrt#22844
Signed-off-by: Nick Hainke <vincent@systemli.org>

Author: DragonBluep

tools/mkimage/Makefile

@@ -26,7 +26,7 @@ define Host/Configure
 		HOSTLDFLAGS="$(HOST_LDFLAGS)" \
 		PKG_CONFIG_EXTRAARGS="--static" \
 		V=$(if $(findstring c,$(OPENWRT_VERBOSE)),1) \
-		tools-only_config
+		tools-only_defconfig
 
 	$(HOST_BUILD_DIR)/scripts/config \
 		--file $(HOST_BUILD_DIR)/.config \