msm-camera:isp: Handle interrupts with zero values

Do not process VFE interrupts if they are genernated with
zero values. Also rate limit error message. This will avoid
unnecessary watchdog timeouts.

Change-Id: I14a433d86f207be7e00992a75e317b24ba31a84b
CRs-fixed: 675181
Signed-off-by: Venu Yeshala <vyeshala@codeaurora.org>