msm: camera: sync: initialize event variable with zero

v4l2_event is a stack buffer, which is not initialized.
This leaves some random byte in it which is kernel sensitive.
By initializing the struct variable with zero removes
vulnerability.

Change-Id: Ib8153a041cd3ad039f35cd27f2e567107f9a7de2
Signed-off-by: Tejas Prajapati <tpraja@codeaurora.org>