ubi: Ensure no fastmap flush after uif_close

On detach UBI attempts to update fastmap after closing user interfaces
but at this point UBI volumes have already been free()'ed and fastmap
can no longer access these data structures.

Signed-off-by: Martin Townsend <mtownsend1973@gmail.com>
Cc: hs@denx.de
Cc: kmpark@infradead.org
Cc: richard@sigma-star.at

drivers/mtd/ubi/fastmap-wl.c

@@ -337,11 +337,6 @@ static void ubi_fastmap_close(struct ubi_device *ubi)
 {
 	int i;
 
-#ifndef __UBOOT__
-	flush_work(&ubi->fm_work);
-#else
-	update_fastmap_work_fn(ubi);
-#endif
 	return_unused_pool_pebs(ubi, &ubi->fm_pool);
 	return_unused_pool_pebs(ubi, &ubi->fm_wl_pool);