autobump: set topic per new gerrit

Gerrit was upgraded and appears to require the topic now be set via the
topic parameter.

Code as-is started giving this error when running script:

remote: Processing changes: refs: 1, done
To ssh://openbmc.gerrit/openbmc/meta-intel
 ! [remote rejected] HEAD -> refs/for/master/autobump (branch master/autobump not found)
error: failed to push some refs to 'ssh://openbmc.gerrit/openbmc/meta-intel'

Tested:
- Verified script properly updated gerrit with autobump topic

Change-Id: I4a68124c324392c3efcf7683b81ac5152aa8a3d9
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/openbmc-autobump/openbmc-autobump.py b/openbmc-autobump/openbmc-autobump.py
index 5165db0..a3612cd 100755
--- a/openbmc-autobump/openbmc-autobump.py
+++ b/openbmc-autobump/openbmc-autobump.py
@@ -174,7 +174,7 @@
 
         git.commit(sh.echo(commit_msg), '-s', '-F', '-', _cwd=meta)
 
-        push_args = ['origin', 'HEAD:refs/for/{}/autobump'.format(args.branch)]
+        push_args = ['origin', 'HEAD:refs/for/{}%topic=autobump'.format(args.branch)]
         if not args.dry_run:
             git.push(*push_args, _cwd=meta)