Btrfs: output warning instead of error when loading free space cache failed

If we fail to load a free space cache, we can rebuild it from the extent tree,
so it is not a serious error, we should not output a error message that
would make the users uncomfortable. This patch uses warning message instead
of it.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/free-space-cache.c

@@ -831,7 +831,7 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
 
 	if (!matched) {
 		__btrfs_remove_free_space_cache(ctl);
-		btrfs_err(fs_info, "block group %llu has wrong amount of free space",
+		btrfs_warn(fs_info, "block group %llu has wrong amount of free space",
 			block_group->key.objectid);
 		ret = -1;
 	}
@@ -843,7 +843,7 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
 		spin_unlock(&block_group->lock);
 		ret = 0;
 
-		btrfs_err(fs_info, "failed to load free space cache for block group %llu",
+		btrfs_warn(fs_info, "failed to load free space cache for block group %llu, rebuild it now",
 			block_group->key.objectid);
 	}