ACPI: fix acpi_hest_firmware_first_pci() caused oops

acpi_hest_firmware_first_pci() could be called when acpi is disabled
and cause system oops.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/hest.c

@@ -123,6 +123,10 @@ int acpi_hest_firmware_first_pci(struct pci_dev *pci)
 {
 	acpi_status status = AE_NOT_FOUND;
 	struct acpi_table_header *hest = NULL;
+
+	if (acpi_disabled)
+		return 0;
+
 	status = acpi_get_table(ACPI_SIG_HEST, 1, &hest);
 
 	if (ACPI_SUCCESS(status)) {