drm: rcar-du: Fix H/V sync signal polarity configuration

drm: rcar-du: Fix H/V sync signal polarity configuration

commit fd1adef3bff0663c5ac31b45bc4a05fafd43d19b upstream.

The VSL and HSL bits in the DSMR register set the corresponding
horizontal and vertical sync signal polarity to active high. The code
got it the wrong way around, fix it.

Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Thong Ho <thong.ho.px@rvc.renesas.com>
Signed-off-by: Nhan Nguyen <nhan.nguyen.yb@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>