[openwrt/openwrt] mediatek: mt7622: don't rely on existing image for sysupgrade

[LEDE Commits]

dangole pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/d640cbac0e76e3638504cb6b239886e8ff75018f

commit d640cbac0e76e3638504cb6b239886e8ff75018f
Author: Daniel Golle <daniel at makrotopia.org>
AuthorDate: Wed Oct 19 19:58:12 2022 +0100

    mediatek: mt7622: don't rely on existing image for sysupgrade
    
    Don't reply on mapped rootfs partition but rather just take what ever
    has been set to the kernel cmdline root= parameter as a hint to decide
    which media to install sysupgrade to on the BananaPi BPi-R64.
    
    Signed-off-by: Daniel Golle <daniel at makrotopia.org>
---
 target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh b/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
index 1036793145..e62eba7ef1 100755
--- a/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
+++ b/target/linux/mediatek/mt7622/base-files/lib/upgrade/platform.sh
@@ -6,8 +6,8 @@ platform_do_upgrade() {
 
 	case "$board" in
 	bananapi,bpi-r64)
-		export_bootdevice
-		export_partdevice rootdev 0
+		local rootdev="$(cmdline_get_var root)"
+		rootdev="${rootdev##*/}"
 		case "$rootdev" in
 		mmc*)
 			CI_ROOTDEV="$rootdev"