Fix memory leak in cocoa accessibility.

Autorelease ("delete later") the created attribute
name array.

Change-Id: I2d7af9eb1fd899f04c8acb90204600a2dd43fa20
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

src/plugins/platforms/cocoa/qcocoaaccessibilityelement.mm

@@ -122,7 +122,7 @@ static QAccessibleInterface *acast(void *ptr)
         [attributes addObject : NSAccessibilityValueAttribute];
     }
 
-    return attributes;
+    return [attributes autorelease];
 }
 
 - (id)accessibilityAttributeValue:(NSString *)attribute {