btrfs: pass btrfs_space_info to btrfs_reserve_data_bytes()

btrfs: pass btrfs_space_info to btrfs_reserve_data_bytes()

Pass struct btrfs_space_info to btrfs_reserve_data_bytes() to allow
reserving the data from multiple data space_info candidates.

This is a preparation for the following commits and there is no functional
change.

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