When invalid cloning configurations were detected during modeset, we
never copied the error code into the return value variable, leading us
to return 0 (success) to userspace.

This regression has been introduced in

commit 50f52756
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Fri Nov 7 13:11:00 2014 -0800

    drm/i915: use compute_config in set_config v4

Testcase: igt/kms_setmode
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86226Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>