ASoC: q6asm: use session lock to avoid use-after-free

It is possible that audio session free and param set happens
simultaneously. Audio client might be freed while param set
is doing wait_event_timeout.
Use session lock to make sure client_free happens after param set.

Change-Id: I0947c309c8e445fa2e220680e329d88bd5fe2418
Signed-off-by: Xiaojun Sang <xsang@codeaurora.org>