ASoC: mediatek: mt8186: set variable aud_pinctrl to static

smatch reports
sound/soc/mediatek/mt8186/mt8186-afe-gpio.c:14:16: warning: symbol
  'aud_pinctrl' was not declared. Should it be static?

This variable is only used in one file so should be static.

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230407115553.1968111-1-trix@redhat.com


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