Close a file descriptor leak in an error case.

PR:		138374
Submitted by:	Patroklos Argyroudis <argp@census-labs.com>
MFC after:	1 week

sys/boot/common/commands.c

@@ -150,6 +150,7 @@ command_help(int argc, char *argv[])
 	break;
     default:
 	command_errmsg = "usage is 'help <topic> [<subtopic>]";
+	close(hfd);
 	return(CMD_ERROR);
     }