msm: camera: crm: Add mutex lock to avoid race condition

mutex lock on crm device adds protection to avoid a scenario
wherein a sequence of calls made from UMD generates a race
condition. A scenario where a call to stop device is
followed by call to unlink, flush and release creates
race condition.

Change-Id: I257306a132047ad490f6fb626c2b7efda42b23d3
Signed-off-by: vhajeri <vhajeri@codeaurora.org>