intel: Set gen7 stencil reference

The stencil reference value for gen7 had uninitialized value.
diff --git a/icd/intel/cmd_pipeline.c b/icd/intel/cmd_pipeline.c
index 81bdb8e..aacfd7f 100644
--- a/icd/intel/cmd_pipeline.c
+++ b/icd/intel/cmd_pipeline.c
@@ -1384,6 +1384,7 @@
 
     if (ds) {
         offset = gen6_DEPTH_STENCIL_STATE(cmd, ds);
+        stencil_ref = ds->cmd_stencil_ref;
         gen7_3dstate_pointer(cmd,
                 GEN7_RENDER_OPCODE_3DSTATE_DEPTH_STENCIL_STATE_POINTERS,
                 offset);