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: NeilBrown <neilb@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 2d82692..cd3a065 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -2029,8 +2029,10 @@
 					   !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);