fixup! fix_trace_division: typos

This is a fixup for commit a73f5fea.

my2to3/fixes/fix_trace_division.py

@@ -39,7 +39,7 @@ class FixTraceDivision(lib2to3.fixer_base.BaseFix):
   def transform(self, node, results):
     lineno = node.get_lineno()
     dividend = node.children[0].clone()
-    if node.prefix == divisor.prefix:
+    if node.prefix == dividend.prefix:
       dividend.prefix = ''
     comma = lib2to3.fixer_util.Comma()
     comma.prefix = prefix = node.children[1].prefix