ASoC: codecs: msm8916-wcd-digital: add support to set_sysclk

This patch adds support to set_sysclk() which can let the sound
card driver to set default mclk rate. In this case MCLK for
internal audio codec is expected to be at 9.6MHz by default.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>