QByteData: use int to return the number of managed QByteArrays

The internal QByteArrays are kept in a QList, so we can use
int to get the count. This matches what operator[] takes,
and gets rid of a bunch of warnings when iterating over a QByteData
using a plain int as a index variable.

Change-Id: Ib44d4101612135b976979a8464442e94706f8736
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qbytedata_p.h

@@ -199,7 +199,7 @@ public:
     }
 
     // the number of QByteArrays
-    inline qint64 bufferCount() const
+    inline int bufferCount() const
     {
         return buffers.length();
     }