msm: camera: isp: Lock around every list access

When multiple threads access a list simulataneously, the
data can become corrupted. To prevent this, make sure
that every time the list is read or written we hold the lock.

CRs-Fixed: 2147202
Change-Id: I6883d1c08507b5a09fbd66ddfa264f79291f94ad
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>