Lolth is the official name of the goddess in GH and FR.
Lloth is a goof by RA Salvatore (love ya, Bob!) that the novels editors didn't catch or correct for quite some time. Later novels explained it (by a sage encountering Drizzt) as a variant name local to Drizzt's home city of Menzoberranzan ... just as the barbarians of Icewind Dale use the name "Tempos" for the god "Tempus."
Just because there are a bunch of novels that propagate that error doesn't mean we should make that error official. Heck, if we did that, we'd have to change how most spells work in the game....