drm/radeon: cleanup properly if mmio mapping fails

commit 0cd9cb76 upstream.

If we fail to map the mmio BAR, skip driver tear down
that requires mmio.

Should fix:
https://bugzilla.kernel.org/show_bug.cgi?id=56541Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/radeon/radeon_kms.c

@@ -39,8 +39,12 @@ int radeon_driver_unload_kms(struct drm_device *dev)
 
 	if (rdev == NULL)
 		return 0;
+	if (rdev->rmmio == NULL)
+		goto done_free;
 	radeon_modeset_fini(rdev);
 	radeon_device_fini(rdev);
+
+done_free:
 	kfree(rdev);
 	dev->dev_private = NULL;
 	return 0;