drm/xe: Fix xe_pt_abort_unbind

When restoring the children PT entries on a bind failure the incorrect
loop index has used resulting in PT entries being leaked. This is shown
by running xe_vm.bind-array-conflict-error-inject on a VRAM device going
into a suspend state after the test completes.

v2:
 - s/childern/children (CI, Matt Auld)

Fixes: a708f650 ("drm/xe: Update PT layer with better error handling")
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240723010230.1652707-1-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_pt.c

@@ -1564,7 +1564,7 @@ static void xe_pt_abort_unbind(struct xe_vma *vma,
 			continue;
 
 		for (j = entry->ofs; j < entry->ofs + entry->qwords; j++)
-			pt_dir->children[i] =
+			pt_dir->children[j] =
 				entries[i].pt_entries[j - entry->ofs].pt ?
 				&entries[i].pt_entries[j - entry->ofs].pt->base : NULL;
 	}