Fix compiler warnings.

qwaylandinputcontext.cpp:57:16: warning: unused parameter 'sym' [-Wunused-parameter]
qwaylanddatadevice.cpp:173:135: warning: 'dragData' may be used uninitialized in this function [-Wmaybe-uninitialized]

Change-Id: Id654360fd9b7fdb572565ad39b664af3355b5e79
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>

src/client/qwaylanddatadevice.cpp

@@ -157,7 +157,7 @@ void QWaylandDataDevice::data_device_enter(uint32_t serial, wl_surface *surface,
 
     QDrag *drag = static_cast<QWaylandDrag *>(QGuiApplicationPrivate::platformIntegration()->drag())->currentDrag();
 
-    QMimeData *dragData;
+    QMimeData *dragData = Q_NULLPTR;
     Qt::DropActions supportedActions;
     if (drag) {
         dragData = drag->mimeData();

src/client/qwaylandinputcontext.cpp

@@ -74,6 +74,7 @@ static Qt::Key toQtKey(uint32_t sym)
         return Qt::Key_unknown;
     }
 #else
+    Q_UNUSED(sym)
     return Qt::Key_unknown;
 #endif
 }