ASoC: wcd9320: set gain after IIR clock is enabled

Gain controller requires an active clock in order
to programme the gain value.
Register a post power up callback handler with
IIR1 clock and re-apply the IIR1 gain register
value in the callback handler.

Change-Id: Idb0640c411b577662cb56fd5e175f6d08c717920
Signed-off-by: SoumyaManagoli <smanag@codeaurora.org>