btrfs: constify fs_info argument of the metadata size calculation helpers

The fs_info argument of the helpers btrfs_calc_insert_metadata_size() and
btrfs_calc_metadata_size() is not modified so it can be const. This will
also allow a new helper function in one of the next patches to have its
fs_info argument as const.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/fs.h

@@ -822,7 +822,7 @@ static inline u64 btrfs_csum_bytes_to_leaves(
  * Use this if we would be adding new items, as we could split nodes as we cow
  * down the tree.
  */
-static inline u64 btrfs_calc_insert_metadata_size(struct btrfs_fs_info *fs_info,
+static inline u64 btrfs_calc_insert_metadata_size(const struct btrfs_fs_info *fs_info,
 						  unsigned num_items)
 {
 	return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * 2 * num_items;
@@ -832,7 +832,7 @@ static inline u64 btrfs_calc_insert_metadata_size(struct btrfs_fs_info *fs_info,
  * Doing a truncate or a modification won't result in new nodes or leaves, just
  * what we need for COW.
  */
-static inline u64 btrfs_calc_metadata_size(struct btrfs_fs_info *fs_info,
+static inline u64 btrfs_calc_metadata_size(const struct btrfs_fs_info *fs_info,
 						 unsigned num_items)
 {
 	return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * num_items;