i965: Fix incorrect comment

There is no intel_miptree_slice_has_hiz function, but there is a
intel_miptree_level_has_hiz function.  I assume that's the correct one
to use.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/mesa/drivers/dri/i965/intel_mipmap_tree.h

@@ -561,7 +561,7 @@ struct intel_mipmap_tree
     * To allocate the hiz buffer, use intel_miptree_alloc_hiz().
     *
     * To determine if hiz is enabled, do not check this pointer. Instead, use
-    * intel_miptree_slice_has_hiz().
+    * intel_miptree_level_has_hiz().
     */
    struct intel_miptree_aux_buffer *hiz_buf;