media: atomisp: add missing media_device_cleanup() in atomisp_unregister_entities()

After the commit 9832e155 ("[media] media-device: split media
initialization and registration"), calling media_device_cleanup()
is needed it seems. However, currently it is missing for the module
unload path.

Note that for the probe failure path, it is already added in
atomisp_register_entities().

This patch adds the missing call of media_device_cleanup() in
atomisp_unregister_entities().

Fixes: a49d2536 ("staging/atomisp: Add support for the Intel IPU v2")
Signed-off-by: Tsuchiya Yuto <kitakar@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>