ASoC: Replace list_empty(&card->codec_dev_list) with !card->instantiated

With componentization we no longer necessarily need a snd_soc_codec struct for a
card. Instead of checking if the card's CODEC list is empty just use
card->instantiated to check if the card has been instantiated yet.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>