dma_alloc_coherent() still needs to support a NULL device

Fix the part of the on-chip memory API that broke this.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

arch/i386/kernel/pci-dma.c

@@ -25,7 +25,7 @@ void *dma_alloc_coherent(struct device *dev, size_t size,
 			   dma_addr_t *dma_handle, int gfp)
 {
 	void *ret;
-	struct dma_coherent_mem *mem = dev->dma_mem;
+	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
 	int order = get_order(size);
 	/* ignore region specifiers */
 	gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);