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.

CRs-Fixed: 2708016
Change-Id: I464c73411596fc562fc7a190ddfa130f23ee487a
Signed-off-by: Tejas Prajapati <tpraja@codeaurora.org>