fix typo and brackets

Author: EvilOlaf

config/boards/rock-3a.conf

@@ -22,7 +22,7 @@ function post_family_config__rock-3a_use_mainline_uboot_except_vendor_and_add_sa
 	BL31=$RKBIN_DIR/$BL31_BLOB $BOOTCONFIG_SATA spl/u-boot-spl.bin u-boot.dtb u-boot.itb;; rkspi_loader_sata.img"
 
 	# use mainline uboot for _current_ and _edge_
-	[[ "$BRANCH" =="vendor" ]] && return 0
+	[[ "${BRANCH}" == "vendor" ]] && return 0
 
 	display_alert "$BOARD" "Mainline U-Boot overrides for $BOARD - $BRANCH" "info"
 	unset BOOTFS_TYPE # fixes armbian-install and unneeded for modern uboot anyway