Leigh Griffiths has promised nothing will stop him in his quest to get fit and firing after netting a late winner in Celtic's 2-0 win over St Johnstone.The striker made his first competitive appearance of the season at McDiarmid Park and grabbed a last-gasp winner after climbing off the bench to rescue his side.Griffiths is desperate to use his all-conquering return as a building block to becoming a regular Celtic contributor once again.The 29-year-old was read the riot act by Neil Lennon in the