quickstart: Fix kernel initramfs configuration

ROOT_UID and ROOT_GID were being asked on build, by setting them with --set-val
this becomes automatic

quickstart.sh

@@ -174,9 +174,10 @@ kernel()
     make $CFLAGS stm32_defconfig
     yes "" | make $CFLAGS oldconfig
     ./scripts/config --file $KERNELBUILDDIR/.config \
-	--set-str INITRAMFS_ROOT_UID 0 \
 	--enable BLK_DEV_INITRD \
 	--set-str INITRAMFS_SOURCE $CPIO_FILE \
+	--set-val INITRAMFS_ROOT_UID 0 \
+	--set-val INITRAMFS_ROOT_GID 0 \
 	--enable RD_GZIP \
 	--enable INITRAMFS_COMPRESSION_GZIP
     make $CFLAGS