Goo VibrationsNow that the public and the Grammy nominating committee see eye to eye on "Iris," the Goo Goo Dolls are reaping the rewards of years spent on the alt-rock fringe.By Tom SinclairThose three grammy nominations for his song ''Iris'' are putting Goo Goo Dolls' singer-guitarist Johnny Rzeznik through some serious changes. Twelve years ago, when the Buffalo-based trio released their first album on an obscure indie label, things were just so much simpler. Back then, the Goo Goo Dolls were just another group of rock-obsessed, guitar-wielding postteens vying for college-radio airplay and