ASoC: wcd9320: Update buck control and mode registers

Leave BUCK control registers as default and set to lower BUCK ref voltage
for avoid pop noise during playback initiation.

CRs-fixed: 506099
Change-Id: I47c068fc8344108dcd5b2c63f8a5c0a5e40a4c8b
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>