MDEV-16955: rocksdb_sys_vars.rocksdb_update_cf_options_basic

... produces "bytes lost" warnings

When rocksdb_validate_update_cf_options() returns an error,
the update won't happen.
Free the copy of the string in this case.

storage/rocksdb/ha_rocksdb.cc

@@ -14314,6 +14314,8 @@ static int rocksdb_validate_update_cf_options(
   // then there's no point to proceed.
   if (!Rdb_cf_options::parse_cf_options(str, &option_map)) {
     my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), "rocksdb_update_cf_options", str);
+    // Free what we've copied with my_strdup above.
+    my_free((void*)(*(const char **)save));
     return HA_EXIT_FAILURE;
   }
   // Loop through option_map and create missing column families