i#3812 avx sigreturn: Update comment on sigreturn crash (#3818)
i#3812 avx sigreturn: Update comment on sigreturn crash (#3818)

Updates a comment which incorrectly speculated that segment bases were
the cause of a sigreturn crash.

Issue: #3812
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio