msm: camera: isp: Remove redundant use of spin lock

Interrupts in activated state machine are already
protected with spin_lock for context. No need to
reuse the spin_lock in interrupt handling routine.

CRs-Fixed: 2538876
Change-Id: Id86e7dc3419861cb8bce143c56923126a3dc3d3e
Signed-off-by: Vishalsingh Hajeri <vhajeri@codeaurora.org>