uboot-envtools: mediatek_filogic: fix BPi-R3 when no OS is installed

Fix accessing the environment in case no OS is installed on the flash
media selected for boot as this is possible when booting initramfs.
In case of relying on the device specified to be mounted as rootfs to
be present, rather just use the kernel cmdline 'root' variable as a
hint to decide where to read/write the U-Boot environment.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/boot/uboot-envtools/files/mediatek_filogic

@@ -13,21 +13,18 @@ board=$(board_name)
 
 case "$board" in
 bananapi,bpi-r3)
-	. /lib/upgrade/common.sh
-	export_bootdevice
-	export_partdevice rootdev 0
-	case "$rootdev" in
-	mmc*)
+	case "$(cmdline_get_var root)" in
+	/dev/mmc*)
 		local envdev=$(find_mmc_part "ubootenv" $rootdev)
 		ubootenv_add_uci_config "$envdev" "0x0" "0x40000" "0x40000" "1"
 		ubootenv_add_uci_config "$envdev" "0x40000" "0x40000" "0x40000" "1"
 		;;
-	mtd*)
+	/dev/mtd*)
 		local envdev=/dev/mtd$(find_mtd_index "u-boot-env")
 		ubootenv_add_uci_config "$envdev" "0x0" "0x20000" "0x20000" "1"
 		ubootenv_add_uci_config "$envdev" "0x20000" "0x20000" "0x20000" "1"
 		;;
-	*)
+	/dev/ubi*)
 		. /lib/upgrade/nand.sh
 		local envubi=$(nand_find_ubi ubi)
 		local envdev=/dev/$(nand_find_volume $envubi ubootenv)