staging: iio: Ensure mutex is correctly unlocked in __iio_push_event

This error was picked up by running the smatch static
checker over all the IIO subsytem.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/industrialio-core.c

@@ -79,11 +79,14 @@ EXPORT_SYMBOL(__iio_change_event);
 	/* Does anyone care? */
 	mutex_lock(&ev_int->event_list_lock);
 	if (test_bit(IIO_BUSY_BIT_POS, &ev_int->handler.flags)) {
-		if (ev_int->current_events == ev_int->max_events)
+		if (ev_int->current_events == ev_int->max_events) {
+			mutex_unlock(&ev_int->event_list_lock);
 			return 0;
+		}
 		ev = kmalloc(sizeof(*ev), GFP_KERNEL);
 		if (ev == NULL) {
 			ret = -ENOMEM;
+			mutex_unlock(&ev_int->event_list_lock);
 			goto error_ret;
 		}
 		ev->ev.id = ev_code;