miner: remove duplicated code (#15968)

miner/miner.go

@@ -105,8 +105,7 @@ out:
 
 func (self *Miner) Start(coinbase common.Address) {
 	atomic.StoreInt32(&self.shouldStart, 1)
-	self.worker.setEtherbase(coinbase)
-	self.coinbase = coinbase
+	self.SetEtherbase(coinbase)
 
 	if atomic.LoadInt32(&self.canStart) == 0 {
 		log.Info("Network syncing, will start miner afterwards")