[nfs] Fix double free bug on error path

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp/oncrpc.c

 
 int oncrpc_call ( struct interface *intf, struct oncrpc_session *session,
                   uint32_t proc_name, const struct oncrpc_field fields[] ) {
-	int              rc;
 	size_t           frame_size;
 	struct io_buffer *io_buf;
 
 	oncrpc_iob_add_fields ( io_buf, header );
 	oncrpc_iob_add_fields ( io_buf, fields );
 
-	rc = xfer_deliver_iob ( intf, io_buf );
-	if ( rc != 0 )
-		free_iob ( io_buf );
-
-	return rc;
+	return xfer_deliver_iob ( intf, iob_disown ( io_buf ) );
 }
 
 size_t oncrpc_compute_size ( const struct oncrpc_field fields[] ) {