piix_pci: fix i440fx data sheet link

It seems that the intel link is unavailable, change it to point to the
qemu site.
Signed-off-by: NLi Qiang <liq3ea@163.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel.apfelbaum@gmail.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>

hw/pci-host/piix.c

@@ -40,7 +40,7 @@
 
 /*
  * I440FX chipset data sheet.
- * http://download.intel.com/design/chipsets/datashts/29054901.pdf
+ * https://wiki.qemu.org/File:29054901.pdf
  */
 
 #define I440FX_PCI_HOST_BRIDGE(obj) \