xen-pt: fix Out-of-bounds read

The array length of s->real_device.io_regions[] is
"PCI_NUM_REGIONS - 1".
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Acked-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/xen/xen_pt_config_init.c

@@ -438,7 +438,7 @@ static int xen_pt_bar_reg_read(XenPCIPassthroughState *s, XenPTReg *cfg_entry,
 
     /* get BAR index */
     index = xen_pt_bar_offset_to_index(reg->offset);
-    if (index < 0 || index >= PCI_NUM_REGIONS) {
+    if (index < 0 || index >= PCI_NUM_REGIONS - 1) {
         XEN_PT_ERR(&s->dev, "Internal error: Invalid BAR index [%d].\n", index);
         return -1;
     }