uboot-envtools: mediatek/mt7622: don't rely on mapped rootfs

Similar to the implementation for the BPi-R3 use the same logic also
for determining the device to look for the U-Boot environment of the
BPi-R64.

Signed-off-by: Daniel Golle <[email protected]>

package/boot/uboot-envtools/files/mediatek_mt7622

@@ -17,16 +17,13 @@ linksys,e8450-ubi)
 	ubootenv_add_uci_config "/dev/ubi0_1" "0x0" "0x1f000" "0x1f000" "1"
 	;;
 bananapi,bpi-r64)
-	. /lib/upgrade/common.sh
-	export_bootdevice
-	export_partdevice rootdev 0
-	case "$rootdev" in
-	mmc*)
+	case "$(cmdline_get_var root)" in
+	/dev/mmc*)
 		local envdev=$(find_mmc_part "ubootenv" $rootdev)
 		ubootenv_add_uci_config "$envdev" "0x0" "0x80000" "0x80000" "1"
 		ubootenv_add_uci_config "$envdev" "0x80000" "0x80000" "0x80000" "1"
 		;;
-	*)
+	/dev/ubi*)
 		ubootenv_add_uci_config "/dev/ubi0_0" "0x0" "0x1f000" "0x1f000" "1"
 		ubootenv_add_uci_config "/dev/ubi0_1" "0x0" "0x1f000" "0x1f000" "1"
 		;;