fix comments

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60442 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

cont.c

@@ -83,8 +83,8 @@ enum context_type {
 struct cont_saved_vm_stack {
     VALUE *ptr;
 #ifdef CAPTURE_JUST_VALID_VM_STACK
-    size_t slen;  /* length of stack (head of th->ec->vm_stack) */
-    size_t clen;  /* length of control frames (tail of th->ec->vm_stack) */
+    size_t slen;  /* length of stack (head of ec->vm_stack) */
+    size_t clen;  /* length of control frames (tail of ec->vm_stack) */
 #endif
 };