drm: make drm_mode_object_find typesafe

I've wasted half a day hunting a bug that could easily be spotted by
gcc. Prevent this from reoccurring.
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/drm_crtc.c

@@ -247,7 +247,8 @@ static void drm_mode_object_put(struct drm_device *dev,
 	mutex_unlock(&dev->mode_config.idr_mutex);
 }
 
-void *drm_mode_object_find(struct drm_device *dev, uint32_t id, uint32_t type)
+struct drm_mode_object *drm_mode_object_find(struct drm_device *dev,
+		uint32_t id, uint32_t type)
 {
 	struct drm_mode_object *obj = NULL;
 

include/drm/drm_crtc.h

@@ -711,7 +711,8 @@ extern void drm_mode_connector_detach_encoder(struct drm_connector *connector,
 					   struct drm_encoder *encoder);
 extern bool drm_mode_crtc_set_gamma_size(struct drm_crtc *crtc,
 					 int gamma_size);
-extern void *drm_mode_object_find(struct drm_device *dev, uint32_t id, uint32_t type);
+extern struct drm_mode_object *drm_mode_object_find(struct drm_device *dev,
+		uint32_t id, uint32_t type);
 /* IOCTLs */
 extern int drm_mode_getresources(struct drm_device *dev,
 				 void *data, struct drm_file *file_priv);