drm/kms: no need to return void value (encoder)

Cc: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_encoder_slave.h

@@ -154,7 +154,7 @@ static inline int drm_i2c_encoder_register(struct module *owner,
  */
 static inline void drm_i2c_encoder_unregister(struct drm_i2c_encoder_driver *driver)
 {
-	return i2c_del_driver(&driver->i2c_driver);
+	i2c_del_driver(&driver->i2c_driver);
 }
 
 void drm_i2c_encoder_destroy(struct drm_encoder *encoder);