ASoC: wcd_cpe: Change to check NULL pointers and update return code

The change is to add NULL pointer checks, update some incorrect
condition checks, and return the correct error code.

Change-Id: Ifd18218a8379572669c7a5561f8a6ecfb5552b02
CRs-fixed: 682558
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>