atl1: disable broken 64-bit DMA

64-bit DMA causes data corruption with atl1.  We don't know why, and Atheros
is working on it.  For now, just use 32-bit DMA.  This is a big hack that is
probably wrong, but it stops the bleeding.

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
Acked-by: Chris Snook <csnook@redhat.com>
Acked-by: Jay Cliburn <jacliburn@bellsouth.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>