soc/intel/common/pcie/rtd3: Update _S0W to use symbol instead of 4

The code is clearer when ACPI_DEVICE_SLEEP_D3_COLD is used instead of
the number 4.

Change-Id: I4b0ade1cd0b4b9cdb59f90f8d455269d0b69ed86
Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56835
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/intel/common/block/pcie/rtd3/rtd3.c

@@ -258,7 +258,7 @@ static void pcie_rtd3_acpi_fill_ssdt(const struct device *dev)
 		acpigen_write_device(acpi_device_name(dev));
 		acpigen_write_ADR(0);
 		acpigen_write_STA(ACPI_STATUS_DEVICE_ALL_ON);
-		acpigen_write_name_integer("_S0W", 4);
+		acpigen_write_name_integer("_S0W", ACPI_DEVICE_SLEEP_D3_COLD);
 
 		dsd = acpi_dp_new_table("_DSD");
 		pkg = acpi_dp_new_table(PCIE_RTD3_STORAGE_UUID);