ACPICA: Fixed possible corruption of global GPE list

Fixed a problem in acpi_ev_delete_gpe_xrupt where the global interrupt
list could be corrupted if the interrupt being removed was at
the head of the list. Reported by Linn Crosetto.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>