drm/i2c: tda998x: free the CEC device on encoder_destroy

The cec i2c device is created in tda998x_encoder_init() when the DRM
driver starts.
This patch frees it when the DRM driver is unloaded.
Tested-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Acked-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: NJean-Francois Moine <moinejf@free.fr>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

drivers/gpu/drm/i2c/tda998x_drv.c

@@ -1094,6 +1094,8 @@ tda998x_encoder_destroy(struct drm_encoder *encoder)
 {
 	struct tda998x_priv *priv = to_tda998x_priv(encoder);
 	drm_i2c_encoder_destroy(encoder);
+	if (priv->cec)
+		i2c_unregister_device(priv->cec);
 	kfree(priv);
 }