cs5520: don't enable VDMA in ->speedproc

There is no need to do it in cs5520_tune_chipset() (->speedproc method)
since it is correctly handled by cs5520_dma_on() (->ide_dma_on method).

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