swiotlb: remove an unecessary NULL check

Smatch complains here:

    lib/swiotlb.c:730 swiotlb_alloc_buffer()
    warn: variable dereferenced before check 'dev' (see line 716)

"dev" isn't ever NULL in this function so we can just remove the check.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

lib/swiotlb.c

@@ -727,7 +727,7 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
 
 out_unmap:
 	dev_warn(dev, "hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
-		(unsigned long long)(dev ? dev->coherent_dma_mask : 0),
+		(unsigned long long)dev->coherent_dma_mask,
 		(unsigned long long)*dma_handle);
 
 	/*