drm: fix fb refcount issue with atomic modesetting

After commit 027b3f8ba9277410c3191d72d1ed2c6146d8a668 ("drm/modes: stop
handling framebuffer special") extra fb refs are left around when doing
atomic modesetting.

The problem is that the new drm_property_change_valid_get() does not
return anything in the '**ref' parameter, which causes
drm_property_change_valid_put() to do nothing.

For some reason this doesn't cause problems with legacy API.

Also, previously the code only set the 'ref' variable for fbs, with this
patch the 'ref' is set for all objects.

Fixes: 027b3f8ba927 ("drm/modes: stop handling framebuffer special")
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -4839,7 +4839,8 @@ bool drm_property_change_valid_get(struct drm_property *property,
 		if (value == 0)
 			return true;
 
-		return _object_find(property->dev, value, property->values[0]) != NULL;
+		*ref = _object_find(property->dev, value, property->values[0]);
+		return *ref != NULL;
 	}
 
 	for (i = 0; i < property->num_values; i++)