Fix some clazy warning

src/kdatepickerpopup.cpp

@@ -173,7 +173,7 @@ KDatePicker *KDatePickerPopup::datePicker() const
     return d->mDatePicker;
 }
 
-void KDatePickerPopup::setDate(const QDate &date)
+void KDatePickerPopup::setDate(QDate date)
 {
     d->mDatePicker->setDate(date);
 }

src/kdatepickerpopup.h

@@ -73,7 +73,7 @@ public Q_SLOTS:
     /**
      * Sets the current @p date.
      */
-    void setDate(const QDate &date);
+    void setDate(QDate date);
 
 Q_SIGNALS:
     /**

src/printing/calprinter.cpp

@@ -74,7 +74,7 @@ void CalPrinter::init(const Akonadi::ETMCalendar::Ptr &calendar)
 
 void CalPrinter::setDateRange(QDate fd, QDate td)
 {
-    for (const auto plugin : mPrintPlugins) {
+    for (const auto plugin : std::as_const(mPrintPlugins)) {
         plugin->setDateRange(fd, td);
     }
 }