msm: camera: sensor: unregister subdev if cpas registration fails

In case if the CPAS registration is failed before freeing the
memory of the subdev, subdev need to be unregistered so that
subdev list entry will not become NULL and other subdev can
be added.

Change-Id: Ibf6c336225c50dc6a5868ec94b076377fe975715
CRs-Fixed: 2708016
Signed-off-by: Shankar Ravi <rshankar@codeaurora.org>