drm/udl: fix line iterator in damage handling

drm/udl: fix line iterator in damage handling

The udl damage handler is supposed to render 'height' lines, but its
iterator has an obvious typo that makes it miss most lines if the
rectangle does not cover 0/0.

Fix the damage handler to correctly render all lines.

This is a fallout from:

    commit 9d07a09caf87dfe6eb908f6441d973aa972e8287
    Author: Noralf Trønnes <noralf@tronnes.org>
    Date:   Thu Apr 28 17:18:37 2016 +0200

        drm/udl: Use drm_fb_helper deferred_io support

Tested-by: poma <poma@gmail.com>
Cc: stable@vger.kernel.org # 4.7+
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>