drivers: hv: dxgkrnl: Add body to macro to silence warnings

If `DXG_TRACE` is configured to be empty and is used from a conditional
like

    if (foo)
      DXG_TRACE("message");

Having no body in the macro causes the if statement to have no body,
which raises a warning. Silence this warning by providing `DXG_TRACE`
with a no-op body under the appropriate configuration.

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>

Author: chessturo

drivers/hv/dxgkrnl/dxgkrnl.h

@@ -1028,7 +1028,7 @@ void dxgk_validate_ioctls(void);
 
 #else
 
-#define DXG_TRACE(...)
+#define DXG_TRACE(...) do { } while (0)
 #define DXG_ERR(fmt, ...) do {					\
 	dev_err(DXGDEV, "%s: " fmt, __func__, ##__VA_ARGS__);	\
 } while (0)