V4L/DVB (13964): tuner-core, fix memory leak

Stanse found a memory leak in tuner_probe. It is not freed/assigned
on all paths. Fix that.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>