ASoC: msm: qdspv2: add result check when audio process fail

A audio_process_event_req is not always to success. Therefore,
check the return value for audio_process_event_req, and
initializ usr_evt before using it.

Bug: 35764875
CRs-Fixed: 2029798
Change-Id: I4adf682575f5f9233a1a1a533f9c6361af8a5bcf
Signed-off-by: kunleiz <kunleiz@codeaurora.org>