i915: Fix another ggtt unit indexing error.

Yeesh.

Author: riastradh

sys/external/bsd/drm2/dist/drm/i915/gt/intel_ggtt.c

@@ -1,12 +1,12 @@
-/*	$NetBSD: intel_ggtt.c,v 1.17 2025/01/26 17:52:23 riastradh Exp $	*/
+/*	$NetBSD: intel_ggtt.c,v 1.18 2025/01/26 18:21:15 riastradh Exp $	*/
 
 // SPDX-License-Identifier: MIT
 /*
  * Copyright © 2020 Intel Corporation
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: intel_ggtt.c,v 1.17 2025/01/26 17:52:23 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: intel_ggtt.c,v 1.18 2025/01/26 18:21:15 riastradh Exp $");
 
 #include <linux/stop_machine.h>
 
@@ -392,7 +392,8 @@ static void gen8_ggtt_clear_range(struct i915_address_space *vm,
 
 #ifdef __NetBSD__
 	for (i = 0; i < num_entries; i++)
-		gen8_set_pte(ggtt->gsmt, ggtt->gsmh, first_entry + i,
+		gen8_set_pte(ggtt->gsmt, ggtt->gsmh,
+		    first_entry + i*sizeof(gen8_pte_t),
 		    scratch_pte);
 #else
 	for (i = 0; i < num_entries; i++)