[IA64] fix __apci_unmap_table

Impact: fix build error

to fix:

  tip/arch/ia64/kernel/acpi.c:203: error: conflicting types for '__acpi_unmap_table'
  tip/include/linux/acpi.h:82: error: previous declaration of '__acpi_unmap_table' was here
  tip/arch/ia64/kernel/acpi.c:203: error: conflicting types for '__acpi_unmap_table'
  tip/include/linux/acpi.h:82: error: previous declaration of '__acpi_unmap_table' was here

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>