btrfs: use GFP_KERNEL in btrfs_calc_avail_data_space

We don't hold any locks here. Inidirectly called from statfs.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -1926,7 +1926,7 @@ static int btrfs_calc_avail_data_space(struct btrfs_fs_info *fs_info,
 	}
 
 	devices_info = kmalloc_array(nr_devices, sizeof(*devices_info),
-			       GFP_NOFS);
+			       GFP_KERNEL);
 	if (!devices_info)
 		return -ENOMEM;