[AGPGART] Add agp-type-to-mask-type method missing from some drivers.

Signed-off-by: Dave Jones <davej@redhat.com>
diff --git a/drivers/char/agp/sis-agp.c b/drivers/char/agp/sis-agp.c
index a00fd48..60342b7 100644
--- a/drivers/char/agp/sis-agp.c
+++ b/drivers/char/agp/sis-agp.c
@@ -140,6 +140,7 @@
 	.free_by_type		= agp_generic_free_by_type,
 	.agp_alloc_page		= agp_generic_alloc_page,
 	.agp_destroy_page	= agp_generic_destroy_page,
+	.agp_type_to_mask_type  = agp_generic_type_to_mask_type,
 };
 
 static struct agp_device_ids sis_agp_device_ids[] __devinitdata =