ata: pata_it821x: Fix possible doc-rotted function names

ata: pata_it821x: Fix possible doc-rotted function names

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

 drivers/ata/pata_it821x.c:346: warning: expecting prototype for it821x_passthru_dma_start(). Prototype was for it821x_passthru_bmdma_start() instead
 drivers/ata/pata_it821x.c:369: warning: expecting prototype for it821x_passthru_dma_stop(). Prototype was for it821x_passthru_bmdma_stop() instead

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210318085150.3131936-6-lee.jones@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>