ACPI: scan: substitute empty_zero_page with helper ZERO_PAGE(0)

Not all zero page implementations use empty_zero_page global pointer so
let's substitute empty_zero_page occurence with helper ZERO_PAGE(0).

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/scan.c

@@ -30,7 +30,7 @@ extern struct acpi_device *acpi_root;
 #define ACPI_BUS_HID			"LNXSYBUS"
 #define ACPI_BUS_DEVICE_NAME		"System Bus"
 
-#define INVALID_ACPI_HANDLE	((acpi_handle)empty_zero_page)
+#define INVALID_ACPI_HANDLE	((acpi_handle)ZERO_PAGE(0))
 
 static const char *dummy_hid = "device";