dma-mapping: remove an unnecessary NULL check

We already dereferenced "dev" when we called get_dma_ops() so this NULL
check is too late.  We're not supposed to pass NULL "dev" pointers to
dma_alloc_attrs().
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/mapping.c

@@ -244,7 +244,7 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 	void *cpu_addr;
 
-	WARN_ON_ONCE(dev && !dev->coherent_dma_mask);
+	WARN_ON_ONCE(!dev->coherent_dma_mask);
 
 	if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
 		return cpu_addr;