ASoC: max98088: Add master clock handling

If master clock is provided through device tree, then update
the master clock frequency during set_sysclk.

Cc: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Acked-by: Tushar Behera <trblinux@gmail.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
[m.felsch@pengutronix.de: move mclk request to i2c_probe]
[m.felsch@pengutronix.de: make use of snd_soc_component_get_bias_level()]
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>