pata_it8213: fix register naming used in it8213_set_piomode()

Rename 'idetm_port' and 'idetm_data' variables to 'master_port'
and 'master_data' respectively to match register naming used in
it8213_set_dmamode() and in ata_piix.c.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>