V4L/DVB (7251): VIDEO_VIVI must depend on VIDEO_DEV

This patch fixes the following compile error with
VIDEO_VIVI=y, VIDEO_DEV=m reported by Toralf Förster:

<--  snip  -->

...
  LD      .tmp_vmlinux1
drivers/built-in.o: In function `vivi_release':
vivi.c:(.text+0x322f5): undefined reference to `video_unregister_device'
vivi.c:(.text+0x32337): undefined reference to `video_device_release'
drivers/built-in.o: In function `vivi_open':
vivi.c:(.text+0x32845): undefined reference to `v4l2_type_names'
drivers/built-in.o: In function `vivi_init':
vivi.c:(.init.text+0x1d20): undefined reference to `video_device_alloc'
vivi.c:(.init.text+0x1d48): undefined reference to `video_register_device'
drivers/built-in.o:(.rodata+0x1b40): undefined reference to
`video_ioctl2'drivers/built-in.o:(.data+0x140c): undefined reference to
`video_device_release'

<--  snip  -->

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>