[media] pwc: Also set alt setting to alt0 when no error occured

isoc_cleanup contains a check to not set the altsetting to alt0 when
the device was unplugged, but the check currently is buggy, and causes
the alt setting to only be set to 0 if an error occured while streaming.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>