sl82c105: add PIO autotune fallback to ->ide_dma_check

Since sl82c105 re-programs DMA/PIO timings for DMA enable/disable, and sets
->autotune this change shouldn't have any other effect than bringing sl82c105
driver in-line with other host drivers wrt ->ide_dma_check implementation.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>