[PATCH v2 3/8] ASoC: mediatek: mt8188: Treat DMIC_GAINx_CUR as non-volatile

[Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>]

The DMIC_GAINx_CUR registers contain the current (as in present) gain of
each DMIC. During capture, this gain will ramp up until a target value
is reached, and therefore the register is volatile since it is updated
automatically by hardware.

However, after capture the register's value returns to the value that
was written to it. So reading these registers returns the current gain,
and writing configures the initial gain for every capture.