CVE-2026-93101

In the Linux kernel, the following vulnerability has been resolved:

media: v4l2-async: Unregister sub-device if asc_list is empty

When my em28xx USB device that uses the i2c tvp5150 driver is
disconnected, it crashes.

The cause is that the tvp5150 i2c module uses v4l2_async, but
the em28xx driver does not since it predates v4l2_async.

In that corner case sd->asc_list is empty, so
v4l2_async_unregister_subdev() never calls v4l2_device_unregister_subdev().

Modify the code so that, if sd->asc_list is empty,
v4l2_device_unregister_subdev() is still called.