The wm9713 currently implements the virtual control for the Mic B Source MUX
using a virtual register. Replace this by using SOC_ENUM_SINGLE_VIRT().
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Acked-by: NCharles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: NMark Brown <broonie@kernel.org>