msm: camera: Add mutex protection while dumping registers

During LDAR dump, LRME, FD registers are dumped. Due to race
conditions or concurrency, there might be a situation
where the hw is in OFF state and still the registers are
read. This will cause aborts on core.
This commit protects the dumping logic with the hw_mutex for
the two drivers.
Also it fixes one crash scenario while dumping the FD registers.

Change-Id: I9b58b43a005a717b059a1a59d64b1810969004aa
Signed-off-by: Gaurav Jindal <gjindal@codeaurora.org>