udlfb: Improve debugging printouts with refresh rate

It is not very helpful to print a list of the same resolutions
without the refresh rate.
Signed-off-by: NBernie Thompson <bernie@plugable.com>

drivers/video/udlfb.c

@@ -1012,7 +1012,8 @@ static int dlfb_is_valid_mode(struct fb_videomode *mode,
 		return 0;
 	}
 
-	pr_info("%dx%d valid mode\n", mode->xres, mode->yres);
+	pr_info("%dx%d @ %d Hz valid mode\n", mode->xres, mode->yres,
+		mode->refresh);
 
 	return 1;
 }