usb: fix up post load checks

Correct post load checks:
1. dev->setup_len == sizeof(dev->data_buf)
    seems fine, no need to fail migration
2. When state is DATA, passing index > len
   will cause memcpy with negative length,
   resulting in heap overflow

First of the issues was reported by dgilbert.
Reported-by: N"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

hw/usb/bus.c

@@ -51,8 +51,8 @@ static int usb_device_post_load(void *opaque, int version_id)
     }
     if (dev->setup_index < 0 ||
         dev->setup_len < 0 ||
-        dev->setup_index >= sizeof(dev->data_buf) ||
-        dev->setup_len >= sizeof(dev->data_buf)) {
+        dev->setup_index > dev->setup_len ||
+        dev->setup_len > sizeof(dev->data_buf)) {
         return -EINVAL;
     }
     return 0;