pata_efar: fix *dma_mask

According to Alan:
>and yes the EFAR does UDMA66.

mwdma:
>Yep - wrong comment. The EFAR is a sort of clone of the PIIX and I
>copied the comment while EFAR don't appear to have copied the
>limitation

Signed-off-by: Erik Inge Bolsø <knan-lkml@anduin.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>