ASoC: Fix null dereference in ak4535_remove()

ak4535_remove() from sound/soc/codecs/ak4535.c calls
i2c_unregister_device() with a possibly null pointer.

This bug was found by smatch (http://repo.or.cz/w/smatch.git/).
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/ak4535.c

@@ -659,6 +659,7 @@ static int ak4535_remove(struct platform_device *pdev)
 	snd_soc_free_pcms(socdev);
 	snd_soc_dapm_free(socdev);
 #if defined(CONFIG_I2C) || defined(CONFIG_I2C_MODULE)
+	if (codec->control_data)
 		i2c_unregister_device(codec->control_data);
 	i2c_del_driver(&ak4535_i2c_driver);
 #endif