V4L/DVB (3927): Fix VIDEO_DEV=m, VIDEO_V4L1_COMPAT=y

If CONFIG_VIDEO_DEV=m and CONFIG_VIDEO_V4L1_COMPAT=y, v4l1-compat should
be built as a module (currently, it isn't built at all leading to
problems with modules using it).

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