drm/meson: Remove unneeded semicolon

Fixes coccicheck warning:

drivers/gpu/drm/meson/meson_plane.c:226:3-4: Unneeded semicolon

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424074949.12309-1-zhengbin13@huawei.com