mediatek: fix writing bananapi bpi-r64 env

Use generic functions to get env partition.

Fixes: 7043e4334f0 ("mediatek: mt7622: improve sysupgrade on MMC")
Signed-off-by: Oskari Lemmela <[email protected]>

package/boot/uboot-envtools/files/mediatek

@@ -17,9 +17,10 @@ linksys,e8450-ubi)
 	ubootenv_add_uci_config "/dev/ubi0_1" "0x0" "0x1f000" "0x1f000" "1"
 	;;
 bananapi,bpi-r64)
-	. /lib/upgrade/platform.sh
-	local rootdev=$(get_rootdev)
-	local envdev=/dev/$(get_partition $rootdev ubootenv)
+	. /lib/upgrade/common.sh
+	export_bootdevice
+	export_partdevice rootdev 0
+	local envdev=/dev/$(get_partition_by_name $rootdev ubootenv)
 	ubootenv_add_uci_config "$envdev" "0x0" "0x80000" "0x80000" "1"
 	ubootenv_add_uci_config "$envdev" "0x80000" "0x80000" "0x80000" "1"
 	;;