msm: camera: isp: Prevent locking same spin_lock twice

The shared_data_lock is used to protect the stream_update count
variable and also the stats enable function. Reduce scope of
lock to only protected variable instead of entire method so that
both places can grab lock without resource conflict.

Change-Id: I1c4d44e6bfa2de73a424df1deda0667416190a1b
Signed-off-by: Harsh Shah <harshs@codeaurora.org>