[AGPGART] Print diagnostic info when failing to determine aperture size on VIA systems.

I've seen this happen a few times, and never got to the bottom of it, so hopefully
this will make things a little easier to diagnose what's going on.
Signed-off-by: Dave Jones <davej@redhat.com>

drivers/char/agp/via-agp.c

@@ -36,6 +36,7 @@ static int via_fetch_size(void)
 			return values[i].size;
 		}
 	}
+	printk(KERN_ERR PFX "Unknown aperture size from AGP bridge (0x%x)\n", temp);
 	return 0;
 }