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<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

drivers/gpu/drm/bridge/lontium-lt9611uxc.c

@@ -855,7 +855,7 @@ static ssize_t lt9611uxc_firmware_show(struct device *dev, struct device_attribu
 {
 	struct lt9611uxc *lt9611uxc = dev_get_drvdata(dev);
 
-	return snprintf(buf, PAGE_SIZE, "%02x\n", lt9611uxc->fw_version);
+	return sysfs_emit(buf, "%02x\n", lt9611uxc->fw_version);
 }
 
 static DEVICE_ATTR_RW(lt9611uxc_firmware);