Silence qdoc warnings

These are internal APIs, so silence qdoc which seems to get confused
by the missing CALLBACK annotation in the implementation.

Change-Id: Iddd9f87257843cc3d43597fe7e6c103aa5e1a646
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Nico Vertriest <nico.vertriest@qt.io>

src/corelib/io/qwindowspipereader.cpp

@@ -307,6 +307,8 @@ void QWindowsPipeReader::startAsyncReadLocked()
 }
 
 /*!
+    \internal
+
     Thread pool callback procedure.
  */
 void QWindowsPipeReader::waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID context,

src/corelib/io/qwindowspipewriter.cpp

@@ -183,6 +183,7 @@ void QWindowsPipeWriter::startAsyncWriteLocked()
 }
 
 /*!
+    \internal
     Thread pool callback procedure.
  */
 void QWindowsPipeWriter::waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID context,