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<[e-mail]>
Signed-off-by: Jiapeng Chong <[e-mail]>
Reviewed-by: Robert Foss <[e-mail]>
Signed-off-by: Robert Foss <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

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

···
 {
 	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);