V4L/DVB (5045): Pvrusb2: Fix heap corruption introduced by radio mods

We can't allocate v4l device structures in a block, since the v4l core
governs when each device actually gets freed.  This bug was introduced
as part of the core radio implementation.  Fix it.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>