soc/amd/block/ivrs: Add NULL check for IVRS

Add NULL check for ivrs pointer before use.

Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Change-Id: Ibeb0ea3bcaa3512a93500588ad4f11046edee61f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75506
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

src/soc/amd/common/block/acpi/ivrs.c

@@ -310,6 +310,11 @@ unsigned long acpi_fill_ivrs(acpi_ivrs_t *ivrs, unsigned long current)
 	struct device *nb_dev;
 	struct device *dev = NULL;
 
+	if (ivrs == NULL) {
+		printk(BIOS_WARNING, "%s: ivrs is NULL\n", __func__);
+		return current;
+	}
+
 	ivhd = &ivrs->ivhd;
 
 	while ((dev = dev_find_path(dev, DEVICE_PATH_DOMAIN)) != NULL) {