ASoC: mt8365: Make non-exported functions static

ASoC: mt8365: Make non-exported functions static

The compilers warn if functions without a prototype are not static so add
appropriate static declarations.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://patch.msgid.link/20240907-asoc-fix-mt8365-build-v1-4-7ad0bac20161@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>