ASoC: ak4642: fixup: mute needs +1 step

ASoC: ak4642: fixup: mute needs +1 step

BugLink: http://bugs.launchpad.net/bugs/981162

commit 1f99e44cf059d2ed43c5a0724fa738b83800f725 upstream.

ak4642 out_tlv is +12.0dB to -115.0 dB, and it supports mute.
But current settings didn't care +1 step for mute.
This patch adds it

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>