uboot-mediatek: fix broken patch

Add missing --- line

Signed-off-by: Felix Fietkau <[email protected]>

package/boot/uboot-mediatek/patches/431-add-xiaomi_redmi-ax6000.patch

@@ -1,3 +1,4 @@
+--- /dev/null
 +++ b/configs/mt7986_xiaomi_redmi-ax6000_defconfig
 @@ -0,0 +1,104 @@
 +CONFIG_ARM=y