drm/radeon/kms: fix screen clearing before fbcon.

This memset_io was added to debug something way back and got
left behind, memset the fb to black so the borders don't be all white.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_fb.c

@@ -248,7 +248,7 @@ int radeonfb_create(struct drm_device *dev,
 	if (ret)
 		goto out_unref;
 
-	memset_io(fbptr, 0xff, aligned_size);
+	memset_io(fbptr, 0x0, aligned_size);
 
 	strcpy(info->fix.id, "radeondrmfb");