ide: use only ->set_pio_mode method for programming PIO modes (take 2)

Use ->set_pio_mode method to program PIO modes in ide_set_xfer_rate()
(the only place which used ->speedproc to program PIO modes) and remove
handling of PIO modes from all ->speedproc implementations.

v2:
* Fix pmac_ide_tune_chipset() comment.

There should be no functionality changes caused by this patch.

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

drivers/ide/pci/siimage.c

@@ -284,13 +284,6 @@ static int siimage_tune_chipset(ide_drive_t *drive, const u8 speed)
 	scsc = is_sata(hwif) ? 1 : scsc;
 
 	switch(speed) {
-		case XFER_PIO_4:
-		case XFER_PIO_3:
-		case XFER_PIO_2:
-		case XFER_PIO_1:
-		case XFER_PIO_0:
-			sil_tune_pio(drive, speed - XFER_PIO_0);
-			return ide_config_drive_speed(drive, speed);
 		case XFER_MW_DMA_2:
 		case XFER_MW_DMA_1:
 		case XFER_MW_DMA_0: