v4l2-ioctl: properly return -EINVAL when parameters are wrong

Whan an ioctl is implemented, but the parameters are invalid,
the error code should be -EINVAL. However, if the ioctl is
not defined, it should return -ENOTTY instead.

Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>