OpenZFS 6551 - cmd/zpool: cleanup gcc warnings

Porting Notes:
- Many of the fixes proposed by this patch were already applied.
In the cases where a different but equivalent fix was made the
code was updated with the OpenZFS version to minimize differences.
- The zpool_get_vdev_by_name() function was previously removed
by commit  235db0a.

Authored by: Igor Kozhukhov <ikozhukhov@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Andy Stormont <astormont@racktopsystems.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Haakan T Johansson <f96hajo@chalmers.se>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/6551
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/b327cd3
Closes #5590

cmd/zpool/zpool_vdev.c

@@ -23,6 +23,7 @@
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2013 by Delphix. All rights reserved.
  * Copyright (c) 2016 Intel Corporation.
+ * Copyright 2016 Igor Kozhukhov <ikozhukhov@gmail.com>.
  */
 
 /*
@@ -776,7 +777,9 @@ get_replication(nvlist_t *nvroot, boolean_t fatal)
 	uint_t c, children;
 	nvlist_t *nv;
 	char *type;
-	replication_level_t lastrep = { 0 }, rep, *ret;
+	replication_level_t lastrep = {0};
+	replication_level_t rep;
+	replication_level_t *ret;
 	boolean_t dontreport;
 
 	ret = safe_malloc(sizeof (replication_level_t));