ACPI / APEI: Get rid of NULL_UUID_LE constant

This is a missed part of the commit 5b53696a
("ACPI / APEI: Switch to use new generic UUID API"), i.e.
replacing old definition with a global constant variable.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/apei/ghes.c

@@ -483,7 +483,7 @@ static void ghes_do_proc(struct ghes *ghes,
 	int sev, sec_sev;
 	struct acpi_hest_generic_data *gdata;
 	guid_t *sec_type;
-	guid_t *fru_id = &NULL_UUID_LE;
+	const guid_t *fru_id = &guid_null;
 	char *fru_text = "";
 
 	sev = ghes_severity(estatus->error_severity);