msm: vidc: Check validity of userspace address

Before writing to a userspace address, verification
of the validity of user space address is required.

Change-Id: I9141e44a6c11aaf3f4d57c08bb0dd26a7b214f34
CRs-fixed: 556356
Signed-off-by: Deepak Verma <dverma@codeaurora.org>