ata: pata_hpt3x2n: Fix possible doc-rotted function name

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

 drivers/ata/pata_hpt3x2n.c:247: warning: expecting prototype for hpt3x2n_bmdma_end(). Prototype was for hpt3x2n_bmdma_stop() instead

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andre Hedrick <andre@linux-ide.org>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>