[media] vivi: Kill BUFFER_TIMEOUT macro

Usage of BUFFER_TIMEOUT has gone in 2008 in 78718e5d (V4L/DVB (7492):
vivi: Simplify the vivi driver and avoid deadlocks), but the macro
remains. Say goodbye to it.

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>