nouveau: don't call pci_dma_supported

Just try to set a 64-bit DMA mask first and retry with the smaller dma_mask
if dma_set_mask failed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Dave Airlie <airlied@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>