V4L/DVB (7489): videobuf-vmalloc.c: Remove buf_release from videobuf_vm_close

Remove the buf_release on vm_close because it will lead to a buffer being
released multiple times since all buffers are already freed under the two
possible cases: device close or STREAMOFF.

Signed-off-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>