btrfs: use btrfs_chunk_max_errors() to replace tolerance calculation

In __btrfs_map_block() we have an assignment to @max_errors using
nr_parity_stripes().

Although it works for RAID56 it's confusing.  Replace it with
btrfs_chunk_max_errors().

Reviewed-by: Johannes Thumshirn <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

fs/btrfs/volumes.c

@@ -6466,7 +6466,7 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
 
 			/* RAID[56] write or recovery. Return all stripes */
 			num_stripes = map->num_stripes;
-			max_errors = nr_parity_stripes(map);
+			max_errors = btrfs_chunk_max_errors(map);
 
 			*length = map->stripe_len;
 			stripe_index = 0;