soc: fsl_asrc: Make some functions static

soc: fsl_asrc: Make some functions static

Fix the following warning:

sound/soc/fsl/fsl_asrc.c:157:5: warning:
symbol 'fsl_asrc_request_pair' was not declared. Should it be static?
sound/soc/fsl/fsl_asrc.c:200:6: warning:
symbol 'fsl_asrc_release_pair' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: ChenTao <chentao107@huawei.com>
Link: https://lore.kernel.org/r/20200507022959.183739-1-chentao107@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>