msm: vidc: Fix handling of ocmem_notifier_register() return value

The ocmem driver might return -EPROBE_DEFER (or any other error)
as a ERR_PTR.  These shouldn't be construed as a valid handle.

Change-Id: Ife5a7e6aaef4f8d9aff3c149cc15e10ce11a4af4
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>
CRs-Fixed: 565882