Fix notificationBusInstance

[ratailor]

This change replaces notificationBusInstance references with notificationsBusInstance for consistency with usage in other operators.

[openshift-ci]

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[fmount]

Thank you, but -1 for now.
As I mentioned in openstack-k8s-operators/openstack-operator#1591 we need to coordinate this with a particular release to not break what is already shipped.

[openshift-ci]

@ratailor: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/precommit-check	c62366f	link	true	/test precommit-check

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[fmount]

Clearly the precommit check indicates that we shouldn't change a parameter that we already released in the same API version, and I think I agree. If we decide to go with this, we should override that check, but I need to check this within the team and circle back to it.