ASoC: dapm: Fix value setting for _ENUM_DOUBLE MUX's second channel

The value for the second channel in _ENUM_DOUBLE (double channel) MUXs
is not correctly updated, due to using the wrong bit shift.

Use the correct bit shift, so both channels toggle together.

Fixes: 3727b496 (ASoC: dapm: Consolidate MUXs and value MUXs)
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>