Covscan fixes

[justin-stephenson]

• First

1. tlog-12/lib/tlog/journal_json_reader.c:0: scope_hint: In function 'tlog_journal_json_reader_init'
2. tlog-12/lib/tlog/journal_json_reader.c:69:17: warning[-Wunused-variable]: unused variable 'namespace'
#      const char *namespace = va_arg(ap, const char *);
#                  ^~~~~~~~~
#    67|       uint64_t until = va_arg(ap, uint64_t);
#    68|       const char * const *match_sym_list = va_arg(ap, const char * const *);
#    69|->     const char *namespace = va_arg(ap, const char *);
#    70|       int sd_rc;
#    71|       tlog_grc grc;

• Second

1. tlog-12/lib/tlog/journal_json_reader.c:69:17: warning[deadcode.DeadStores]: Value stored to 'namespace' during its initialization is never read
#    67|       uint64_t until = va_arg(ap, uint64_t);
#    68|       const char * const *match_sym_list = va_arg(ap, const char * const *);
#    69|->     const char *namespace = va_arg(ap, const char *);
#    70|       int sd_rc;
#    71|       tlog_grc grc;