drm/rockchip: Remove unneeded semicolon

Fixes coccicheck warning:

drivers/gpu/drm/rockchip/cdn-dp-reg.c:604:2-3: Unneeded semicolon
drivers/gpu/drm/rockchip/cdn-dp-reg.c:622:2-3: Unneeded semicolon
drivers/gpu/drm/rockchip/cdn-dp-reg.c:703:2-3: Unneeded semicolon

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424074410.1070-1-zhengbin13@huawei.com