drivers/misc: add protection for probe order changes

HDCP driver can get probed before the SDE driver causing
empty device handles to be stored in the device related
structures.

Add protection for such cases by checking the validitiy
of the handle and storing it if necessary.

CRs-Fixed: 2181269
Change-Id: I65d574788900db06e168ba0d4014c575f8f4cda6
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>