[media] fix compilation with both V4L2 and I2C as 'm'

When config options are:
	CONFIG_VIDEO_DEV=y
	CONFIG_VIDEO_V4L2=m
	CONFIG_I2C=m

Compilation breaks, as reported by:
	https://bugzilla.kernel.org/show_bug.cgi?id=55681



Before changeset 7b34be71,
no compilation errors occurred. However, the I2C code there at
v4l2-device was incorrectly disabled.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>