CMake: Add a missing break

Detected by GCC7

Change-Id: Ia9a76df63c28d4f4ebf3e20f70ab39224115b5a1
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/cmakeprojectmanager/cmakesettingspage.cpp

@@ -124,8 +124,10 @@ public:
                     name += tr(" (Default)");
                 return name;
             }
-            case 1: return m_executable.toUserOutput();
+            case 1:
+                return m_executable.toUserOutput();
             }
+            break;
 
         case Qt::FontRole: {
             QFont font;