ata: pata_atiixp: Fix a function name and supply description for 'pio'

Fixes the following W=1 kernel build warning(s):

 drivers/ata/pata_atiixp.c:103: warning: Function parameter or member 'pio' not described in 'atiixp_set_pio_timing'
 drivers/ata/pata_atiixp.c:241: warning: expecting prototype for atiixp_dma_stop(). Prototype was for atiixp_bmdma_stop() instead

Cc: Jens Axboe <axboe@kernel.dk>
Cc: ATI Inc <hyu@ati.com>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>