[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>