ata: optimize struct ata_force_param size

Optimize struct ata_force_param size by:
- using u8 for cbl and spd_limit fields
- using u16 for lflags field

Code size savings on m68k arch using (modified) atari_defconfig:

   text    data     bss     dec     hex filename
before:
  41064     573      40   41677    a2cd drivers/ata/libata-core.o
after:
  40654     573      40   41267    a133 drivers/ata/libata-core.o

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>