broadcom/vc5: Fix pasteo in front stencil ref value setup.

Fixes piglit masked-clear.
diff --git a/src/gallium/drivers/vc5/vc5_emit.c b/src/gallium/drivers/vc5/vc5_emit.c
index ecb1b25..72b5d85 100644
--- a/src/gallium/drivers/vc5/vc5_emit.c
+++ b/src/gallium/drivers/vc5/vc5_emit.c
@@ -437,7 +437,7 @@
                         cl_emit_with_prepacked(&job->bcl, STENCIL_CONFIG,
                                                vc5->zsa->stencil_front, config) {
                                 config.stencil_ref_value =
-                                        vc5->stencil_ref.ref_value[1];
+                                        vc5->stencil_ref.ref_value[0];
                         }
                 }