iio: core: Use sysfs_emit()

sysfs_emit() is preferred over raw s*printf() for sysfs attributes since it
knows about the sysfs buffer specifics and has some built-in checks for
size and alignment.

This patch converts the places in the IIO core that follow the pattern of

   return s*printf(...)

to

   return sysfs_emit(...)

This covers the new places that have been introduced where sprintf() is
used for formatting sysfs output since the last time this was done in
commit 83ca56b6 ("iio: core: Use sysfs_emit() (trivial bits)").
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211216185217.1054495-2-lars@metafoo.deSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-buffer.c

@@ -1383,9 +1383,9 @@ static ssize_t direction_show(struct device *dev,
 
 	switch (buffer->direction) {
 	case IIO_BUFFER_DIRECTION_IN:
-		return sprintf(buf, "in\n");
+		return sysfs_emit(buf, "in\n");
 	case IIO_BUFFER_DIRECTION_OUT:
-		return sprintf(buf, "out\n");
+		return sysfs_emit(buf, "out\n");
 	default:
 		return -EINVAL;
 	}

drivers/iio/industrialio-core.c

@@ -747,7 +747,7 @@ static ssize_t iio_read_channel_label(struct device *dev,
 		return indio_dev->info->read_label(indio_dev, this_attr->c, buf);
 
 	if (this_attr->c->extend_name)
-		return sprintf(buf, "%s\n", this_attr->c->extend_name);
+		return sysfs_emit(buf, "%s\n", this_attr->c->extend_name);
 
 	return -EINVAL;
 }