ACPI / numa: Fix acpi_get_node() prototype

acpi_get_node() takes an acpi_handle, not an "acpi_handle *".  This
fixes the prototype and the definitions.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>