au1xxx: fix au1xxx_set_pio_mode()

Set transfer mode on the device before programming the host controller for
the new timings (matches what auide_tune_chipset() is doing wrt DMA modes).

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