[sushi] utils: fix setting fullscreen icon name

[Cosimo Cecchi <cosimoc src gnome org>]

commit 120b0047b9f1ca05dc266b2603afb8d7b570bb36
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Sat Jun 22 15:17:48 2019 -0700

    utils: fix setting fullscreen icon name
    
    We were setting the icon_name property on the wrong widget.

 src/ui/utils.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/ui/utils.js b/src/ui/utils.js
index 293dd9a..21901df 100644
--- a/src/ui/utils.js
+++ b/src/ui/utils.js
@@ -73,8 +73,8 @@ function createFullscreenButton(renderer) {
     return createToolButton(renderer, 'view-fullscreen-symbolic', (button) => {
         renderer.toggleFullscreen();
         if (renderer.fullscreen)
-            button.icon_name = 'view-restore-symbolic';
+            button.image.icon_name = 'view-restore-symbolic';
         else
-            button.icon_name = 'view-fullscreen-symbolic';
+            button.image.icon_name = 'view-fullscreen-symbolic';
     });
 }