btrfs: qgroup: Cleanup old inaccurate facilities

Cleanup the old facilities which use old btrfs_qgroup_reserve() function
call, replace them with the newer version, and remove the "__" prefix in
them.

Also, make btrfs_qgroup_reserve/free() functions private, as they are
now only used inside qgroup codes.

Now, the whole btrfs qgroup is swithed to use the new reserve facilities.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 490c9e2..a7dc456 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3034,8 +3034,8 @@
 	BUG_ON(cluster->start != cluster->boundary[0]);
 	mutex_lock(&inode->i_mutex);
 
-	ret = __btrfs_check_data_free_space(inode, cluster->start,
-					    cluster->end + 1 - cluster->start);
+	ret = btrfs_check_data_free_space(inode, cluster->start,
+					  cluster->end + 1 - cluster->start);
 	if (ret)
 		goto out;
 
@@ -3056,8 +3056,8 @@
 			break;
 		nr++;
 	}
-	__btrfs_free_reserved_data_space(inode, cluster->start,
-					 cluster->end + 1 - cluster->start);
+	btrfs_free_reserved_data_space(inode, cluster->start,
+				       cluster->end + 1 - cluster->start);
 out:
 	mutex_unlock(&inode->i_mutex);
 	return ret;