drm/i915/migrate: fix length calculation

No need to insert PTEs for the PTE window itself, also foreach expects a
length not an end offset, which could be gigantic here with a second
engine.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211206112539.3149779-3-matthew.auld@intel.com

drivers/gpu/drm/i915/gt/intel_migrate.c

@@ -133,7 +133,7 @@ static struct i915_address_space *migrate_vm(struct intel_gt *gt)
 			goto err_vm;
 
 		/* Now allow the GPU to rewrite the PTE via its own ppGTT */
-		vm->vm.foreach(&vm->vm, base, base + sz, insert_pte, &d);
+		vm->vm.foreach(&vm->vm, base, d.offset - base, insert_pte, &d);
 	}
 
 	return &vm->vm;