drm/sun4i: Remove unneeded semicolon in sun8i_mixer.c

Fixes coccicheck warning:

drivers/gpu/drm/sun4i/sun8i_mixer.c:289:3-4: Unneeded semicolon
drivers/gpu/drm/sun4i/sun8i_mixer.c:292:2-3: Unneeded semicolon
drivers/gpu/drm/sun4i/sun8i_mixer.c:302:3-4: Unneeded semicolon
drivers/gpu/drm/sun4i/sun8i_mixer.c:305:2-3: Unneeded semicolon

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/1576317091-24968-2-git-send-email-zhengbin13@huawei.com