drm/i915: Propagate invalid setcrtc cloning errors back to userspace

drm/i915: Propagate invalid setcrtc cloning errors back to userspace

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 11f58c8af5f7aae9c218d80decec2174928940b9
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=86226
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>