kirkwood: fix Linksys upgrade, restore config step

It appears that the refactor of the upgrade process for NAND devices
resulted in the nand_do_upgrade_success step not being called for
devices using the linksys.sh script. As a result, configuration was
not preserved over sysupgrade steps.

This restores the preservation of configs for kirkwood devices using the
linksys.sh script.

Fixes: e25e6d8 ("base-files: fix and clean up nand sysupgrade code")
Fixes: #12298
Signed-off-by: Michael Trinidad <trinidude4@hotmail.com>

target/linux/kirkwood/base-files/lib/upgrade/linksys.sh

@@ -68,7 +68,12 @@ platform_do_upgrade_linksys() {
 			CI_UBIPART="rootfs2"
 		fi
 
-		nand_upgrade_tar "$1"
+		if nand_upgrade_tar "$1" ; then
+			nand_do_upgrade_success
+		else
+			nand_do_upgrade_failed
+		fi
+
 	}
 	[ "$magic_long" = "27051956" ] && {
 		get_image "$1" | mtd write - $part_label