um: Neaten vu_err macro definition

Defining a macro with ... and __VA_ARGS__ (without ##) can cause
compilation errors if a macro use does not have additional args.

Add ## to __VA_ARGS__ in the macro definition.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/virtio_uml.c

@@ -74,7 +74,7 @@ struct virtio_uml_vq_info {
 
 extern unsigned long long physmem_size, highmem;
 
-#define vu_err(vu_dev, ...)	dev_err(&(vu_dev)->pdev->dev, __VA_ARGS__)
+#define vu_err(vu_dev, ...)	dev_err(&(vu_dev)->pdev->dev, ##__VA_ARGS__)
 
 /* Vhost-user protocol */