[media] tm6000: fix vbuf may be used uninitialized

In commit 8aff8ba9, most of the manipulations to vbuf inside
copy_streams were gated on if !dev->radio, but one place that touches
vbuf lays outside those gates -- a memcpy of vbuf isn't NULL. If we
initialize vbuf to NULL, that memcpy will never happen in the case where
we do have dev->radio, and otherwise, in the !dev->radio case, the code
behaves exactly like it did prior to 8aff8ba9

.

While we're at it, also fix an incorrectly indented closing brace for
one of the sections touching vbuf that is conditional on !dev->radio.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>