acpi: mark INVARIANTS variables as __diagused

Fixes INVARIANTS build with Clang 15, which previously failed due to
set-but-not-used variable warnings.

Reviewed by:	jhb
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D36096

sys/dev/acpica/acpi_pci_link.c

@@ -719,7 +719,7 @@ acpi_pci_link_srs_from_crs(struct acpi_pci_link_softc *sc, ACPI_BUFFER *srsbuf)
 	ACPI_RESOURCE *end, *res;
 	ACPI_STATUS status;
 	struct link *link;
-	int i, in_dpf;
+	int i __diagused, in_dpf;
 
 	/* Fetch the _CRS. */
 	ACPI_SERIAL_ASSERT(pci_link);
@@ -861,7 +861,7 @@ acpi_pci_link_route_irqs(device_t dev)
 	ACPI_BUFFER srsbuf;
 	ACPI_STATUS status;
 	struct link *link;
-	int i;
+	int i __diagused;
 
 	ACPI_SERIAL_ASSERT(pci_link);
 	sc = device_get_softc(dev);