Ensure controller or namespace node name is specified before trying to

access it.

While here, also fix the identify usage message to show the -v and -x
parameters.

Sponsored by:	Intel
MFC after:	3 days

sbin/nvmecontrol/identify.c

@@ -259,6 +259,10 @@ identify(int argc, char *argv[])
 
 	while (getopt(argc, argv, "vx") != -1) ;
 
+	/* Check that a controller or namespace was specified. */
+	if (optind >= argc)
+		identify_usage();
+
 	target = argv[optind];
 
 	optreset = 1;

sbin/nvmecontrol/nvmecontrol.h

@@ -38,7 +38,7 @@
 "       nvmecontrol devlist\n"
 
 #define IDENTIFY_USAGE							       \
-"       nvmecontrol identify <controller id|namespace id>\n"
+"       nvmecontrol identify [-x [-v]] <controller id|namespace id>\n"
 
 #define PERFTEST_USAGE							       \
 "       nvmecontrol perftest <-n num_threads> <-o read|write>\n"	       \