Drivers: hv: utils: fix hvt_op_poll() return value on transport destroy

The return type of hvt_op_poll() is unsigned int and -EBADF is
inappropriate, poll functions return POLL* statuses.
Reported-by: NDexuan Cui <decui@microsoft.com>
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/hv_utils_transport.c

@@ -109,7 +109,7 @@ static unsigned int hvt_op_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &hvt->outmsg_q, wait);
 
 	if (hvt->mode == HVUTIL_TRANSPORT_DESTROY)
-		return -EBADF;
+		return POLLERR | POLLHUP;
 
 	if (hvt->outmsg_len > 0)
 		return POLLIN | POLLRDNORM;