intel: Fix performance regression in Lightsmark since HiZ changes.

Since the refactor in d7b33309fe, depth
in the miptree changed from 1 to 6, so we always decided it didn't
match, and we would relayout to something that would still not
"match".

Improves performance 23.8% (+/- 1.1%, n=4)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=43329

src/mesa/drivers/dri/intel/intel_mipmap_tree.c

@@ -345,6 +345,9 @@ intel_miptree_match_image(struct intel_mipmap_tree *mt,
 
    intel_miptree_get_dimensions_for_image(image, &width, &height, &depth);
 
+   if (mt->target == GL_TEXTURE_CUBE_MAP)
+      depth = 6;
+
    /* Test image dimensions against the base level image adjusted for
     * minification.  This will also catch images not present in the
     * tree, changed targets, etc.