msm: vidc: WARN_ON() reveals fuction addresses

There is a security vulnerability where function addresses are
printed in kernel message if WARN_ON() is invoked implicitly.
WARN_ON() call is made explicit to avoid this issue.

Change-Id: If75581803adf62cb9bda3784ad1d4f4088e0d797
Signed-off-by: Sanjay Singh <sisanj@codeaurora.org>