scc_pata: make use of scc_dma_sff_read_status()

Make consistent use of scc_dma_sff_read_status() throughout the driver.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>