dsp: Reslove audiodlkm code warning

q6afe: sanitize variables, fill proper error codes/messages
q6voice: modify func return value type
Initialized mutex while probing was not destroyed
while removing the module

Change-Id: I951e957bd8f15fa300e867472fb38755a7a80dec
Signed-off-by: Jing Wang <jingwa@codeaurora.org>