Minor cleanup in snowball consensus

snow/consensus/snowball/flat.go

@@ -34,7 +34,7 @@ func (f *Flat) Parameters() Parameters { return f.params }
 // RecordPoll implements the Consensus interface
 func (f *Flat) RecordPoll(votes ids.Bag) {
 	if pollMode, numVotes := votes.Mode(); numVotes >= f.params.Alpha {
-		f.nnarySnowball.RecordSuccessfulPoll(pollMode)
+		f.RecordSuccessfulPoll(pollMode)
 	} else {
 		f.RecordUnsuccessfulPoll()
 	}

snow/consensus/snowball/nnary_snowflake.go

@@ -51,7 +51,7 @@ func (sf *nnarySnowflake) RecordSuccessfulPoll(choice ids.ID) {
 		return // This instace is already decided.
 	}
 
-	if preference := sf.nnarySlush.Preference(); preference.Equals(choice) {
+	if preference := sf.Preference(); preference.Equals(choice) {
 		sf.confidence++
 	} else {
 		// confidence is set to 1 because there has already been 1 successful