ASoC: tas2552: Fix kernel crash when the codec is loaded but not part of a card

If the card is not part of any card the tas_data->codec is NULL since it is
set only during snd_soc_codec_driver.probe, which is not yet called.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org