Fix return description in PyThreadState_Ensure().

Author: ZeroIntensity

peps/pep-0788.rst

@@ -434,10 +434,8 @@ replace :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release`.
     if the interpreter matches *lock*, it is attached, and otherwise a new
     thread state is created.
 
-    The old thread state is stored as a thread view in *\*thread*, and is
-    to be restored by :c:func:`PyThreadState_Release`.
-
-    Return ``0`` on success, and ``-1`` without an exception set on failure.
+    Return a non-zero thread view of the old thread state on success, and
+    ``0`` on failure.
 
 .. c:function:: void PyThreadState_Release(PyThreadView lock)