x86/amd-iommu: Remove double NULL check in check_device

dev was tested just above, so drop the second test.
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NJoerg Roedel <joerg.roedel@amd.com>

arch/x86/kernel/amd_iommu.c

@@ -118,7 +118,7 @@ static bool check_device(struct device *dev)
 		return false;
 
 	/* No device or no PCI device */
-	if (!dev || dev->bus != &pci_bus_type)
+	if (dev->bus != &pci_bus_type)
 		return false;
 
 	devid = get_device_id(dev);