[caffe2] fix wrong comment (#42735)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42735

We use reduced precision only for embedding table (not for momentum) in RowWiseSparseAdagrad

Test Plan: .

Reviewed By: jianyuh

Differential Revision: D23003939

fbshipit-source-id: 062290d94b160100bc4c2f48b797833819f8e88a
diff --git a/caffe2/sgd/rowwise_adagrad_fused.h b/caffe2/sgd/rowwise_adagrad_fused.h
index ea4babb..5430b97 100644
--- a/caffe2/sgd/rowwise_adagrad_fused.h
+++ b/caffe2/sgd/rowwise_adagrad_fused.h
@@ -126,7 +126,7 @@
  * and evaluation results.
  */
 template <
-    typename Tdata, // embedding and momentum types
+    typename Tdata, // embedding types
     typename T, // everything else
     typename TLengths,
     typename rowWiseAdagradT,
@@ -390,7 +390,7 @@
 };
 
 template <
-    typename Tdata, // embedding and momentum types
+    typename Tdata, // embedding types
     typename T, // everything else
     typename TLengths,
     typename rowWiseAdagradT>
@@ -694,7 +694,7 @@
 };
 
 template <
-    typename Tdata, // embedding and momentum types
+    typename Tdata, // embedding types
     typename T, // everything else
     typename TLengths,
     typename rowWiseAdagradT>