Core/Spells: Correct a mistake in HOT aura procs

A crash fix was added in 3e0d2e49448ae5d53baefa0ef3b2df4542aae1dd
but the usage of spellProcEvent itself was incorrect, we should instead use spellProto of aura to be procced
Merge pull request #11984 from Unholychick/patch-1

Core/Spells: Correct a mistake in HoT aura procs