Access using the hybrid state framework requires the list to be protected by
a mutex.

Thanks to Michael Krufky <mkrufky@linuxtv.org> for reporting this during a
code review.
Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>