V4L/DVB (4348): Fix: compile for radio aimslab and aztech with V4L2 only

All radio devices use an obsolete mode of opening/release driver.
Since this is not V4L1 core, better to keep the method available for more
time than to rewrite open/release without a radio device to test, since the
newer method is much more complex than the previous one (although providing
support for multiple opens and multiple devices).

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>