iio: iio_event_getfd -- fix ev_int build failure

Fix build failure in staging iio driver:

.../drivers/staging/iio/industrialio-core.c: In function 'iio_event_getfd':
.../drivers/staging/iio/industrialio-core.c:262:32: error:
			'ev_int' undeclared (first use in this function)

Also convert the rest of the function to use the new variable.
Signed-off-by: NAndy Whitcroft <apw@canonical.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/staging/iio/industrialio-core.c

@@ -242,25 +242,24 @@ static const struct file_operations iio_event_chrdev_fileops = {
 
 static int iio_event_getfd(struct iio_dev *indio_dev)
 {
+	struct iio_event_interface *ev_int = indio_dev->event_interface;
 	int fd;
 
-	if (indio_dev->event_interface == NULL)
+	if (ev_int == NULL)
 		return -ENODEV;
 
-	mutex_lock(&indio_dev->event_interface->event_list_lock);
-	if (test_and_set_bit(IIO_BUSY_BIT_POS,
-			     &indio_dev->event_interface->flags)) {
-		mutex_unlock(&indio_dev->event_interface->event_list_lock);
+	mutex_lock(&ev_int->event_list_lock);
+	if (test_and_set_bit(IIO_BUSY_BIT_POS, &ev_int->flags)) {
+		mutex_unlock(&ev_int->event_list_lock);
 		return -EBUSY;
 	}
-	mutex_unlock(&indio_dev->event_interface->event_list_lock);
+	mutex_unlock(&ev_int->event_list_lock);
 	fd = anon_inode_getfd("iio:event",
-				&iio_event_chrdev_fileops,
-				indio_dev->event_interface, O_RDONLY);
+				&iio_event_chrdev_fileops, ev_int, O_RDONLY);
 	if (fd < 0) {
-		mutex_lock(&indio_dev->event_interface->event_list_lock);
+		mutex_lock(&ev_int->event_list_lock);
 		clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags);
-		mutex_unlock(&indio_dev->event_interface->event_list_lock);
+		mutex_unlock(&ev_int->event_list_lock);
 	}
 	return fd;
 }