x86_64: Fail dma_alloc_coherent on dma less devices

This should fix an oops with PCMCIA PATA devices

	http://bugzilla.kernel.org/show_bug.cgi?id=8424

This is not a full fix for the problem, but probably
still the right thing to do.

[ I'm almost certain it's *not* the right thing to do, but it avoids an
  oops, and I want comments from others on what the right thing would
  actually be..  I suspect we should just remove the use of dma_mask
  entirely in this function, and just use coherent_dma_mask.  - Linus ]
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86_64/kernel/pci-dma.c

@@ -82,6 +82,10 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
 	if (dma_mask == 0)
 		dma_mask = DMA_32BIT_MASK;
 
+	/* Device not DMA able */
+	if (dev->dma_mask == NULL)
+		return NULL;
+
 	/* Don't invoke OOM killer */
 	gfp |= __GFP_NORETRY;