UBI: bugfix in ubi_wl_flush()

Use the _safe variant because we're iterating over a list where items get
deleted and freed.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/wl.c

@@ -1718,12 +1718,12 @@ int ubi_wl_flush(struct ubi_device *ubi, int vol_id, int lnum)
 	       vol_id, lnum, ubi->works_count);
 
 	while (found) {
-		struct ubi_work *wrk;
+		struct ubi_work *wrk, *tmp;
 		found = 0;
 
 		down_read(&ubi->work_sem);
 		spin_lock(&ubi->wl_lock);
-		list_for_each_entry(wrk, &ubi->works, list) {
+		list_for_each_entry_safe(wrk, tmp, &ubi->works, list) {
 			if ((vol_id == UBI_ALL || wrk->vol_id == vol_id) &&
 			    (lnum == UBI_ALL || wrk->lnum == lnum)) {
 				list_del(&wrk->list);