ASoC: fsl_asrc: Fix -Wmissing-prototypes warning

ASoC: fsl_asrc: Fix -Wmissing-prototypes warning

COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64

sound/soc/fsl/fsl_asrc.c:557:18: warning: no previous prototype for function 'fsl_asrc_get_dma_channel' [-Wmissing-prototypes]
struct dma_chan *fsl_asrc_get_dma_channel(struct fsl_asrc_pair *pair, bool dir)
                 ^
sound/soc/fsl/fsl_asrc.c:557:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
struct dma_chan *fsl_asrc_get_dma_channel(struct fsl_asrc_pair *pair, bool dir)
^
static

Fixes: be7bd03f0201 ("ASoC: fsl_asrc: Move common definition to fsl_asrc_common")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: shengjiu wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1590397412-12966-1-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>