ASoC: dapm: Use SND_SOC_DAPM_INIT_REG_VAL in SND_SOC_DAPM_MUX

SND_SOC_DAPM_MUX() doesn't currently initialize the .mask field. This
results in the mux never affecting HW, since no bits are ever set or
cleared. Fix SND_SOC_DAPM_MUX() to use SND_SOC_DAPM_INIT_REG_VAL() to
set up the reg, shift, on_val, and off_val fields like almost all other
SND_SOC_xxx() macros. It looks like this was a "typo" in the fixed
commit linked below.

This makes the speakers on the Toshiba AC100 (PAZ00) laptop work again.

Fixes: de9ba98b ("ASoC: dapm: Make widget power register settings more flexible")
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: <stable@vger.kernel.org> # v3.12+