iio: light: Convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:
drivers/iio/light/veml6030.c:131:8-16: WARNING:
use scnprintf or sprintf

Signed-off-by: Tian Tao <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/light/veml6030.c

···
 		return -EINVAL;
 	}
 
-	return snprintf(buf, PAGE_SIZE, "%s\n", period_values[x]);
+	return sysfs_emit(buf, "%s\n", period_values[x]);
 }
 
 static IIO_DEVICE_ATTR_RO(in_illuminance_period_available, 0);