[media] tm6000: Fix check for interrupt endpoint

Checking for &dev->int_in is useless because it returns the address of
the embedded struct tm6000_endpoint, which will always be positive and
therefore true.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>