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: Bernie Thompson <[e-mail]>

drivers/video/udlfb.c

···
 		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;
 }