wacom: Use right function to find whether stylus has eraser tip

We are looking for paired styli that act as standalone erasers, this is
not what we are looking for here.

panels/wacom/cc-wacom-tool.c

@@ -305,5 +305,5 @@ cc_wacom_tool_get_has_eraser (CcWacomTool *tool)
 {
 	g_return_val_if_fail (CC_IS_WACOM_TOOL (tool), FALSE);
 
-	return libwacom_stylus_has_eraser (tool->wstylus);
+	return libwacom_stylus_is_eraser (tool->wstylus);
 }