Fix getMessageForBlockHash comment

Author: qdm12

lib/grandpa/tracker_commits.go

@@ -95,9 +95,10 @@ func (ct *commitsTracker) delete(blockHash common.Hash) {
 	delete(ct.mapping, blockHash)
 }
 
-// getMessageForBlockHash returns the commit messages
-// for a particular block hash from the tracker.
-// It returns nil if the block hash does not exist.
+// getMessageForBlockHash returns a pointer to the
+// commit message for a particular block hash from
+// the tracker. It returns nil if the block hash
+// does not exist in the tracker
 func (ct *commitsTracker) getMessageForBlockHash(
 	blockHash common.Hash) (message *CommitMessage) {
 	data, ok := ct.mapping[blockHash]