The mask should define the bits to change in the register, not the
bits to preserve.

This fixes the inadvertent changes of the "Headphone Analog Gain"
value during mute/unmute.
Signed-off-by: NNicolas Schichan <nschichan@freebox.fr>
Acked-by: NBrian Austin <brian.austin@cirrus.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>