ASoC: wcd9335: Update TX gain correctly after decimator enable

Gain for TX decimator block needs to be set after the
corresponding decimator is enabled. Otherwise, gain will
not take affect. Apply the gain by reading from regmap cache
to the codec decimator hardware after decimator is enabled.

CRs-fixed: 982473
Change-Id: Ib2d189b56e58b038a343fc974e6e3b8ef29f982d
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>