10687 Service routine cast changes need smatch fixes

@@ -2,10 +2,11 @@
  * sppp.c - Solaris STREAMS PPP multiplexing pseudo-driver
  *
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  * Copyright (c) 2016 by Delphix. All rights reserved.
+ * Copyright 2019, Joyent, Inc.
  *
  * Permission to use, copy, modify, and distribute this software and its
  * documentation is hereby granted, provided that the above copyright
  * notice appears in all copies.
  *

@@ -1840,11 +1841,11 @@
 sppp_lrsrv(queue_t *q)
 {
         mblk_t *mp;
 
         while ((mp = getq(q)) != NULL)
-                sppp_lrput(q, mp);
+                (void) sppp_lrput(q, mp);
         return (0);
 }
 
 /*
  * sppp_recv_nondata()