treewide: sysupgrade: don't use $ARGV in platform_do_upgrade()

stage2 passes image path to platform_do_upgrade() as an argument so it
can be simply accessed using $1

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit 8b4bc7abe0)
[rmilecki: dropping ARGV without this change broke sysupgrade]
Fixes: 6ac62c4b6c ("base-files: don't set ARGV and ARGC")

target/linux/gemini/base-files/lib/upgrade/platform.sh

@@ -19,7 +19,7 @@ platform_do_upgrade() {
 	case "$board" in
 	dlink,dir-685)
 		PART_NAME=firmware
-		default_do_upgrade "$ARGV"
+		default_do_upgrade "$1"
 		;;
 	esac
 }