drm: renesas: shmobile: Use drm_crtc_handle_vblank()

Replace the call to the legacy drm_handle_vblank() function with a call
to the new drm_crtc_handle_vblank() helper.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/bef278cc9b7536505f41faaa2f13184d9354fa7e.1694767209.git.geert+renesas@glider.be