x86: fsp: Don't enable FSP graphics if booted from coreboot

This driver cannot work when booted from coreboot, since the FSP
information is not available. Disable it in that case, so that the
coreboot video driver can be used instead.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/x86/lib/fsp/fsp_graphics.c

@@ -87,7 +87,7 @@ static int fsp_video_probe(struct udevice *dev)
 	int ret;
 
 	if (!ll_boot_init())
-		return 0;
+		return -ENODEV;
 
 	printf("Video: ");