gitreview branch update

After a release has been created and repositories have been branched & tagged:

• voltha-helm-charts

• voltha-system-tests

Update the .gitreview file on the voltha-x.y release branch so commits are directed to branch=voltha-x.y rather than the default voltha=master

[gerrit]
host=gerrit.opencord.org
port=29418
project=voltha-helm-charts.git
defaultremote=origin
defaultbranch=master

[gerrit]
host=gerrit.opencord.org
port=29418
project=voltha-helm-charts.git
defaultremote=origin
defaultbranch=voltha-2.11