[2.7] Fix misleading mentions of tp_size in comments (GH-9138)

Many type object initializations labeled a field "tp_size" in the
comment, but the name of that field is tp_basicsize..
(cherry picked from commit 0e0bc4e221f592f305d335faf5f8046484eb9238)

Co-authored-by: Peter Eisentraut <peter@eisentraut.org>
diff --git a/Modules/md5module.c b/Modules/md5module.c
index 103da14..dd90a22 100644
--- a/Modules/md5module.c
+++ b/Modules/md5module.c
@@ -236,7 +236,7 @@
 static PyTypeObject MD5type = {
     PyVarObject_HEAD_INIT(NULL, 0)
     "_md5.md5",                   /*tp_name*/
-    sizeof(md5object),            /*tp_size*/
+    sizeof(md5object),            /*tp_basicsize*/
     0,                            /*tp_itemsize*/
     /* methods */
     (destructor)md5_dealloc,  /*tp_dealloc*/