drm: bridge: convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:

drivers/gpu/drm/bridge/lontium-lt9611uxc.c:858:8-16: WARNING: use
scnprintf or sprintf.

Reported-by: Abaci <Robot&lt;abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1612689000-64577-1-git-send-email-jiapeng.chong@linux.alibaba.com