eth: fix minor grammar issue in comment (#18091)

eth/handler.go

@@ -653,7 +653,7 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 			trueHead = request.Block.ParentHash()
 			trueTD   = new(big.Int).Sub(request.TD, request.Block.Difficulty())
 		)
-		// Update the peers total difficulty if better than the previous
+		// Update the peer's total difficulty if better than the previous
 		if _, td := p.Head(); trueTD.Cmp(td) > 0 {
 			p.SetHead(trueHead, trueTD)