msm: camera: cpas: Add protection for concurrent execution

This change adds mutex lock in register client to protect
client data. It also sets probe done flag to false during
dev remove to force all other functions that might be
invoked in parallel to return without any action.

Change-Id: Iaf4bf65c8a1e0bedf86952817512fcf0f0a71070
Signed-off-by: Venkat Chinta <vchinta@codeaurora.org>