[PATCH] libata: Use ATA_FLAG_PIO_POLLING for pdc_adma

pdc_adma was overlooked and broken by the irq-pio patch:
Only HSM_ST_LAST interrupts should be delivered to this LLDD.

Adding ATA_FLAG_PIO_POLLING to pdc_adma fixes the problem (temporarily),
before we convert the irq handler of pdc_adma to handle all interrupts.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>