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 e375882406d0cc24030746638592004755ed4ae0
    Author: Noralf Trønnes <[email protected]>
    Date:   Thu Apr 28 17:18:37 2016 +0200

        drm/udl: Use drm_fb_helper deferred_io support

Tested-by: poma <[email protected]>
Cc: [email protected] # 4.7+
Reviewed-by: Daniel Vetter <[email protected]>
Signed-off-by: David Herrmann <[email protected]>
Reviewed-by: Eric Engestrom <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>