usb: fix boot paths

The fw paths for USB devices that SeaBIOS computes are off-by-one,
because QEMU builds those paths with a numbering that starts from one
(see usb_fill_port and usb_hub_initfn in QEMU).  Fix that so that
the numbering agrees.
diff --git a/src/boot.c b/src/boot.c
index 119f290..93928d3 100644
--- a/src/boot.c
+++ b/src/boot.c
@@ -191,9 +191,9 @@
     for (i=56; i>0; i-=8) {
         int port = (path >> i) & 0xff;
         if (port != 0xff)
-            p += snprintf(p, desc+sizeof(desc)-p, "/hub@%x", port);
+            p += snprintf(p, desc+sizeof(desc)-p, "/hub@%x", port+1);
     }
-    snprintf(p, desc+sizeof(desc)-p, "/*@%x", (u32)(path & 0xff));
+    snprintf(p, desc+sizeof(desc)-p, "/*@%x", (u32)(path & 0xff)+1);
     return find_prio(desc);
 }