cbuildbot: fix typo

bin/cbuildbot.py

 #!/usr/bin/python
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import errno
 import optparse
 import os
 import shutil
@@ skipping 89 matching lines @@
   RunCommand(['./build_packages'], cwd=cwd)
 
 def _UprevAllPackages(buildroot):
   cwd = os.path.join(buildroot, 'src', 'scripts')
   RunCommand(['./enter_chroot.sh', '--', './cros_mark_all_as_stable',
               '--tracking_branch="cros/master"'],
              cwd=cwd)
 
 def _UprevPackages(buildroot, revisionfile):
   revisions = None
-  if (revision_file):
+  if (revisionfile):
     rev_file = revisionfile.open(revisionfile)
     revisions = rev_file.read()
     rev_file.close()
 
   # Note:  Revisions == "None" indicates a Force Build.
   if revisions and revisions != 'None':
     print 'CBUILDBOT - Revision list found %s' % revisions
     print 'Revision list not yet propagating to build, marking all instead'
 
   _UprevAllPackages(buildroot)
@@ skipping 64 matching lines @@
       _UprevPush(buildroot)
       _UprevCleanup(buildroot)
   except:
     # something went wrong, cleanup (being paranoid) for next build
     if clobber:
       RunCommand(['sudo', 'rm', '-rf', buildroot], print_cmd=False)
     raise
 
 if __name__ == '__main__':
     main()