aubinator: Store a pointer from gen_group back to gen_spec.

When decoding a structure field within a group, we may want to look up
that structure type.  Having a gen_spec pointer makes it easy to do so.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/tools/decoder.c

@@ -180,6 +180,7 @@ create_group(struct parser_context *ctx, const char *name, const char **atts)
    if (name)
       group->name = xstrdup(name);
 
+   group->spec = ctx->spec;
    group->group_offset = 0;
    group->group_count = 0;
 

src/intel/tools/decoder.h

@@ -60,6 +60,7 @@ struct gen_field_iterator {
 };
 
 struct gen_group {
+   struct gen_spec *spec;
    char *name;
    int nfields;
    struct gen_field **fields;