ASoC: core: fix shift used for second item in snd_soc_get_enum_double

Incorrect shift value was being used to extract the second item.

Signed-off-by: Jaswinder Jassal <jjassal@opensource.wolfsonmicro.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>