btrfs: simplify memcpy either of metadata_uuid or fsid

There is a helper which provides either metadata_uuid or fsid as per
METADATA_UUID flag. So use it.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -841,15 +841,8 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 		    found_transid > fs_devices->latest_generation) {
 			memcpy(fs_devices->fsid, disk_super->fsid,
 					BTRFS_FSID_SIZE);
-
-			if (has_metadata_uuid)
-				memcpy(fs_devices->metadata_uuid,
-				       disk_super->metadata_uuid,
-				       BTRFS_FSID_SIZE);
-			else
-				memcpy(fs_devices->metadata_uuid,
-				       disk_super->fsid, BTRFS_FSID_SIZE);
-
+			memcpy(fs_devices->metadata_uuid,
+			       btrfs_sb_fsid_ptr(disk_super), BTRFS_FSID_SIZE);
 			fs_devices->fsid_change = false;
 		}
 	}