ASoC: fsl_micfil: Remove set but not used variable 'osr'

Fixes gcc '-Wunused-but-set-variable' warning:

sound/soc/fsl/fsl_micfil.c: In function 'get_clk_div':
sound/soc/fsl/fsl_micfil.c:154:6: warning: variable 'osr' set but not used [-Wunused-but-set-variable]

It is never used since introduction in
commit 47a70e6f ("ASoC: Add MICFIL SoC Digital Audio Interface driver.")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>