ASoC: sam9g20_wm8731: Use static DAI format setup

Set the dai_fmt field in the dai_link struct instead of manually calling
snd_soc_dai_fmt(). This makes the code cleaner and shorter.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>