xhci: add asserts to help with static code analysis

Most callers of xhci_port_update() and xhci_wakeup() pass in a pointer
to an array entry and can never be NULL but add two defensive asserts
to protect against future changes (e.g. adding a new port speed, etc.)
adding a path through xhci_lookup_port() that could result in the
return of a NULL XHCIPort.
Signed-off-by: NLiam Merwick <liam.merwick@oracle.com>
Message-id: 1549460216-25808-3-git-send-email-liam.merwick@oracle.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/hcd-xhci.c

@@ -2607,6 +2607,7 @@ static void xhci_port_update(XHCIPort *port, int is_detach)
 {
     uint32_t pls = PLS_RX_DETECT;
 
+    assert(port);
     port->portsc = PORTSC_PP;
     if (!is_detach && xhci_port_have_device(port)) {
         port->portsc |= PORTSC_CCS;
@@ -3215,6 +3216,7 @@ static void xhci_wakeup(USBPort *usbport)
     XHCIState *xhci = usbport->opaque;
     XHCIPort *port = xhci_lookup_port(xhci, usbport);
 
+    assert(port);
     if (get_field(port->portsc, PORTSC_PLS) != PLS_U3) {
         return;
     }