drm/rcar-du: Update plane pitch in .mode_set_base() operation

When setting a new frame buffer with the mode set base operation the
pitch value might change. Set the hardware plane pitch register at the
same time as the plane base address in the rcar_du_plane_update_base()
function to make sure the pitch value always matches the frame buffer.

Cc: stable@vger.kernel.org
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>