The vpif_config struct was renamed to vpif_display_config, but there
is still a stray vpif_config *config pointer in vpif_display.c, preventing
it from compiling.

Remove this old duplicate pointer.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>