asoc: codecs: wcd938x: Fix volatile register function

Fix the volatile register function to return false
if the registers are not volatile so that the reads
will happen from cache and this improves read timing.

Change-Id: I73149be3855be09a71ad61a6f3143038a7ba029b
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>