drm: Fix drm_cvt_mode() for interlaced modes.

The calculated vdisplay was half the right value.

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 6b4d2dc..9e54925 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -146,7 +146,7 @@
 	if (margins)
 		vmargin = vdisplay_rnd * CVT_MARGIN_PERCENTAGE / 1000;
 
-	drm_mode->vdisplay = vdisplay_rnd + 2 * vmargin;
+	drm_mode->vdisplay = vdisplay + 2 * vmargin;
 
 	/* Interlaced */
 	if (interlaced)