soc/amd/*/northbridge,root_complex: simplify mmconf_resource index

In the northbridge's and root complex' read_resources function, the
mmconf resource used the number of the MMIO_CONF_BASE MSR as index which
might be misleading. Instead use idx++ as a unique index for this
resource.

TEST=Resource allocator doesn't complain and no related warnings or
errors in dmesg. The update_constraints console output changes like
expected:

Before: PCI: 00:00.0 c0010058 base f8000000 limit fbffffff mem (fixed)
After: PCI: 00:00.0 06 base f8000000 limit fbffffff mem (fixed)

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Id66c6153fad86bed36db7bd2455075f4a0850750
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62545
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
diff --git a/src/soc/amd/stoneyridge/northbridge.c b/src/soc/amd/stoneyridge/northbridge.c
index 04472dc..0a80648 100644
--- a/src/soc/amd/stoneyridge/northbridge.c
+++ b/src/soc/amd/stoneyridge/northbridge.c
@@ -57,6 +57,7 @@
 
 static void read_resources(struct device *dev)
 {
+	unsigned int idx = 0;
 	struct resource *res;
 
 	/*
@@ -64,7 +65,7 @@
 	 * It is not honored by the coreboot resource allocator if it is in
 	 * the CPU_CLUSTER.
 	 */
-	mmconf_resource(dev, MMIO_CONF_BASE);
+	mmconf_resource(dev, idx++);
 
 	/* NB IOAPIC2 resource */
 	res = new_resource(dev, IO_APIC2_ADDR); /* IOAPIC2 */