ASoC: davinci-mcasp: Set .symmetric_rates = 1 in snd_soc_dai_driver

The TX and RX direction share the same bit clock and frame sync, so
the samplerate must be the same to both directions.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>