ASoC: TSCS42xx: make functions pll_event and dac_event static

The functions pll_event and dac_event are local to the source and do
not need to be in global scope, so make them static.

Cleans up sparse warnings:
symbol 'pll_event' was not declared. Should it be static?
symbol 'dac_event' was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Steven Eckhoff <steven.eckhoff.opensource@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>