qsavefile_p.h: fix missing qsavefile.h include

This causes

  qsavefile_p.h:28:22: error: unknown type name 'QSaveFile'
      Q_DECLARE_PUBLIC(QSaveFile)
                       ^

when qsavefile_p.h is included before qsavefile.h was.

Make the header self-sufficient by incuding the Public class' header,
too, as is customary.

Amends e993df8.

Pick-to: 6.5 6.2 5.15
Task-number: QTBUG-126219
Change-Id: I17eb2a357bf1ef7ef5b5e3a3e56c4a921ba30951
Reviewed-by: Thiago Macieira <[email protected]>
(cherry picked from commit ad6e4df)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
(cherry picked from commit e2880c7)

src/corelib/io/qsavefile_p.h

@@ -15,7 +15,7 @@
 // We mean it.
 //
 
-#include <QtCore/qglobal.h>
+#include <QtCore/qsavefile.h>
 
 #ifndef QT_NO_TEMPORARYFILE