md/bitmap: call bitmap_file_unmap once bitmap_storage_alloc returns -ENOMEM

It is possible that bitmap_storage_alloc could return -ENOMEM,
and some member inside store could be allocated such as filemap.

To avoid memory leak, we need to call bitmap_file_unmap to free
those members in the bitmap_resize.
Reviewed-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/bitmap.c

@@ -2029,8 +2029,10 @@ int bitmap_resize(struct bitmap *bitmap, sector_t blocks,
 					   !bitmap->mddev->bitmap_info.external,
 					   mddev_is_clustered(bitmap->mddev)
 					   ? bitmap->cluster_slot : 0);
-	if (ret)
+	if (ret) {
+		bitmap_file_unmap(&store);
 		goto err;
+	}
 
 	pages = DIV_ROUND_UP(chunks, PAGE_COUNTER_RATIO);