[PATCH] Fix dm_io.c oops in low memory conditions.

If you call drivers/md/dm-io.c:resize_pool on an empty pool and
mempool_create is unable to make the pool, the condition is not handled
correctly, resulting in an oops in mempool_destroy.

Trivial fix.

drivers/md/dm-io.c

@@ -267,7 +267,7 @@ static int resize_pool(unsigned int new_ios)
 		/* create new pool */
 		_io_pool = mempool_create(new_ios, alloc_io, free_io, NULL);
 		if (!_io_pool)
-			r = -ENOMEM;
+			return -ENOMEM;
 
 		r = bio_set_init(&_bios, "dm-io", 512, 1);
 		if (r) {