[media] v4l2-ioctl: simplify debug code

The core debug code can now be simplified since all the write-only ioctls are
now const and will not modify the data they pass to the drivers.
So instead of logging write-only ioctls before the driver is called this can
now be done afterwards, which is cleaner when it comes to error reporting as
well.
This also fixes a logic error in the debugging code where there was one 'else'
too many.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>