Fix check in db_bench for num shard bits to match check in LRUCache (#8110)

Summary:
The check in db_bench for table_cache_numshardbits was 0 < bits <= 20, whereas the check in LRUCache was 0 < bits < 20.  Changed the two values to match to avoid a crash in db_bench on a null cache.

Fixes https://github.com/facebook/rocksdb/issues/7393

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8110

Reviewed By: zhichao-cao

Differential Revision: D27353522

Pulled By: mrambacher

fbshipit-source-id: a414bd23b5bde1f071146b34cfca5e35c02de869

tools/db_bench_tool.cc

@@ -1008,8 +1008,8 @@ DEFINE_uint64(compression_max_dict_buffer_bytes,
 
 static bool ValidateTableCacheNumshardbits(const char* flagname,
                                            int32_t value) {
-  if (0 >= value || value > 20) {
-    fprintf(stderr, "Invalid value for --%s: %d, must be  0 < val <= 20\n",
+  if (0 >= value || value >= 20) {
+    fprintf(stderr, "Invalid value for --%s: %d, must be  0 < val < 20\n",
             flagname, value);
     return false;
   }