[PATCH] libata: set PIO-0 after successful EH reset

Set ata_device->pio_mode to XFER_PIO_0 after a successful reset.  This
is to keep EH resets consistent with probe resets as updated by the
commit b6079ca4.  Note that, with
soon-to-follow hotplug update, EH resets will include probe resets.

Signed-off-by: Tejun Heo <htejun@gmail.com>