pata_it8213: fix wrong MWDMA timings being programmed

Clear old MWDMA timings before programming new ones (IT8213
is a single port host so there is no need to check ap->port_no).

This change should be safe as this is how we have been doing
things in IDE it8213 host driver for years.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/pata_it8213.c

@@ -210,7 +210,7 @@ static void it8213_set_dmamode (struct ata_port *ap, struct ata_device *adev)
 			master_data &= 0xFF4F;  /* Mask out IORDY|TIME1|DMAONLY */
 			master_data |= control << 4;
 			pci_read_config_byte(dev, 0x44, &slave_data);
-			slave_data &= (0x0F + 0xE1 * ap->port_no);
+			slave_data &= 0xF0;
 			/* Load the matching timing */
 			slave_data |= ((timings[pio][0] << 2) | timings[pio][1]) << (ap->port_no ? 4 : 0);
 			pci_write_config_byte(dev, 0x44, slave_data);