and return ENODATA instead of EAGAIN

Set the new capability flags in G_TUNER and return ENODATA if no channels
were found.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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