msm: camera: vfe: memset irq mask array to zero

IRQ mask can store some junk value which can cause
spurious interrupts. This change initializes
the irq mask array to zero.

Change-Id: I4f4f6292813f61520aaa9adac018f360ce957ebc
Signed-off-by: Vishalsingh Hajeri <vhajeri@codeaurora.org>