ASoC: fsl_micfil: use define for OSR default value

The OSR (OverSampling Rate) setting is set once to the default value
and never changed throughout the driver. Nevertheless the value is
read back from the register for further calculations. Just use the
default value because we know what we have written.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shengjiu Wang <shengjiu.wang@gmail.com>
Link: https://lore.kernel.org/r/20220414162249.3934543-14-s.hauer@pengutronix.de


Signed-off-by: Mark Brown <broonie@kernel.org>