mediatek: fix sysupgrade on MTK7986 rfba AP

A line in platform.sh was accidentally removed when adding support
for the Bananapi BPi-R3.
Re-add it to fix sysupgrade on the MTK7986 rfba AP.

Fixes: a96382c1bb ("mediatek: add support for Bananapi BPi-R3")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/filogic/base-files/lib/upgrade/platform.sh

@@ -25,6 +25,7 @@ platform_do_upgrade() {
 		esac
 		;;
 	*)
+		nand_do_upgrade "$1"
 		;;
 	esac
 }