usb: rearrange usb_ep_get()

There is no need to calculate the 'eps' variable in usb_ep_get()
if 'ep' is the control endpoint.  Instead the calculation should
be done after validating the input before returning an entry
indexed by the endpoint 'ep'.
Signed-off-by: NLiam Merwick <liam.merwick@oracle.com>
Reviewed-by: NDarren Kenny <Darren.Kenny@oracle.com>
Reviewed-by: NMark Kanda <Mark.Kanda@oracle.com>
Reviewed-by: NAmeya More <ameya.more@oracle.com>
Message-id: 1549460216-25808-2-git-send-email-liam.merwick@oracle.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/core.c

@@ -720,12 +720,12 @@ struct USBEndpoint *usb_ep_get(USBDevice *dev, int pid, int ep)
     if (dev == NULL) {
         return NULL;
     }
-    eps = (pid == USB_TOKEN_IN) ? dev->ep_in : dev->ep_out;
     if (ep == 0) {
         return &dev->ep_ctl;
     }
     assert(pid == USB_TOKEN_IN || pid == USB_TOKEN_OUT);
     assert(ep > 0 && ep <= USB_MAX_ENDPOINTS);
+    eps = (pid == USB_TOKEN_IN) ? dev->ep_in : dev->ep_out;
     return eps + ep - 1;
 }