[media] cx18: Bump driver version to 1.5.0

To simplify maintainer support of this driver, bump the version to
1.5.0 - this will be the first version that is expected to support
mmap() for raw video frames.

Signed-off-by: Simon Farnsworth <simon.farnsworth@onelan.co.uk>
Acked-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>