btrfs: pass btrfs_io_geometry into btrfs_max_io_len

Instead of passing three individual members of 'struct btrfs_io_geometry'
into btrfs_max_io_len(), pass a pointer to btrfs_io_geometry.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>