ASoC: remove unneeded dai->driver->ops check

On soc_add_dai(), it uses null_dai_ops if driver doesn't have
its own ops. This means, dai->driver->ops never been NULL.
dai->driver->ops check is not needed.
This patch removes it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>