ASoC: rt5645: mic-in detection threshold modification

Modify mic-in detection threshold for better performance.

Signed-off-by: Jack Yu <jack.yu@realtek.com>
Link: https://msgid.link/r/b7614d9e38054aa6ad8efa620edb4162@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>