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 <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1618216751-1678-3-git-send-email-tiantao6@hisilicon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/veml6030.c

@@ -128,7 +128,7 @@ static ssize_t in_illuminance_period_available_show(struct device *dev,
 		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);