drm: Fix deadlock due to getconnector locking changes

In commit ccfc0865
Author: Rob Clark <robdclark@gmail.com>
Date:   Thu Dec 18 16:01:48 2014 -0500

    drm: tweak getconnector locking

We need to extend the locking to cover connector->state reading for
atomic drivers, but the above commit was a bit too eager and also
included the fill_modes callback. Which on i915 on old platforms using
load detection needs to acquire modeset locks, resulting in a deadlock
on output probing.

Reported-by: Marc Finet <m.dreadlock@gmail.com>
Cc: Marc Finet <m.dreadlock@gmail.com>
Cc: robdclark@gmail.com
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>