Fix empty size for hash_zch_bucket (meta-pytorch#3447)

Summary: Pull Request resolved: meta-pytorch#3447

Reviewed By: yumin829928

Differential Revision: D84292465

fbshipit-source-id: f781c0b1a0fa0c08a453e6b81c196564a4449b4d

Author: chaodengusc

torchrec/modules/hash_mc_modules.py

@@ -305,7 +305,7 @@ def __init__(
 
         self._max_probe = max_probe
         self._buckets = total_num_buckets
-        self.register_buffer("_hash_zch_bucket", torch.tensor(total_num_buckets))
+        self.register_buffer("_hash_zch_bucket", torch.tensor([total_num_buckets]))
         # Do not need to store in buffer since this is created and consumed
         # at each step https://fburl.com/code/axzimmbx
         self._evicted_indices = []