mediatek: fix platform_copy_config()

Also use env variables exported by export_fitblk_rootdev() in
platform_copy_config().

Fixes: 4448d6325f ("mediatek: make use of common uImage.FIT upgrade functions")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/filogic/base-files/lib/upgrade/platform.sh

@@ -218,11 +218,9 @@ platform_copy_config() {
 	bananapi,bpi-r3-mini|\
 	bananapi,bpi-r4|\
 	bananapi,bpi-r4-poe)
-		case "$(fitblk_get_bootdev)" in
-		mmcblk*)
+		if [ "$CI_METHOD" = "emmc" ]; then
 			emmc_copy_config
-			;;
-		esac
+		fi
 		;;
 	acer,predator-w6|\
 	glinet,gl-mt2500|\

target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh

@@ -86,7 +86,7 @@ platform_check_image() {
 platform_copy_config() {
 	case "$(board_name)" in
 	bananapi,bpi-r64)
-		if fitblk_get_bootdev | grep -q mmc; then
+		if [ "$CI_METHOD" = "emmc" ]; then
 			emmc_copy_config
 		fi
 		;;