ASoC: fix compilation warnings after enabling LLVM

After enabling compilation with LLVM for audio drivers,
some assignment warnings are reported. Add this change
to resolve the compilation warnings.

Change-Id: I571b2e210053bc0b80d65cd272ce1751e0ed10fb
Signed-off-by: Meng Wang <mengw@codeaurora.org>
Signed-off-by: Soumya Managoli <smanag@codeaurora.org>