McuSupport: Avoid mix of dir separator styles for CMake parameter

Qt Creator's CMake plugin would otherwise (since recently) open that
"sync" dialog if a configuration path contains back slashes.

Change-Id: I2e333604e22158bdb61c2ca8eb65911295383b52
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/mcusupport/mcusupportoptionspage.cpp

@@ -160,6 +160,7 @@ void McuSupportOptionsPage::apply()
         package->writeToSettings();
 
     QTC_ASSERT(m_options->toolchainPackage, return);
+    QTC_ASSERT(m_options->qulSdkPackage, return);
 
     const QVector<BoardOptions*> validBoards = m_options->validBoards();