msm: camera2: cpp: Reset payload for VIDIOC_MSM_CPP_GET_EVENTPAYLOAD

In 32-bit / 64-bit compat mode, the kernel32 structure populated
manually from kernel64 structure. This kernel32 is copied directly
to user32 structure. Any padding in kernel32 is not set to 0. This
results in invalid data being copied to user32 structure.

Change-Id: I58ae65bcbb32cd0f11127533d53f5a2d731032b2
Signed-off-by: Rajakumar Govindaram <rajakuma@codeaurora.org>