ASoC: bolero: Fix voice activation not working on SWR MICs

Voice Activation is not working from second time on SWR
MICs. Make tx macro registers related to SWR MIC as
volatile to resolve the issue.

Change-Id: Iac52af37d32b53ada193d855949b345da0e47d9c
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>