[subset] Update gsub to use glyphset() method of subset plan.

src/hb-ot-layout-gsub-table.hh

diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 33b8f0e..cc10634 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -105,7 +105,7 @@
   bool subset (hb_subset_context_t *c) const
   {
     TRACE_SUBSET (this);
-    const hb_set_t &glyphset = *c->plan->glyphset;
+    const hb_set_t &glyphset = *c->plan->glyphset ();
     const hb_map_t &glyph_map = *c->plan->glyph_map;
     hb_vector_t<GlyphID> from;
     hb_vector_t<GlyphID> to;
@@ -202,7 +202,7 @@
   bool subset (hb_subset_context_t *c) const
   {
     TRACE_SUBSET (this);
-    const hb_set_t &glyphset = *c->plan->glyphset;
+    const hb_set_t &glyphset = *c->plan->glyphset ();
     const hb_map_t &glyph_map = *c->plan->glyph_map;
     hb_vector_t<GlyphID> from;
     hb_vector_t<GlyphID> to;