firmware: arm_scmi: Simplify scmi_devm_notifier_unregister

firmware: arm_scmi: Simplify scmi_devm_notifier_unregister

Unregistering SCMI notifications using the managed devres interface can be
done providing as a reference simply the previously successfully registered
notification block since it could have been registered only on one kernel
notification_chain: drop any reference to SCMI protocol, events and
sources.

Devres internal helpers can search for the provided notification block
reference and, once found, the associated devres object will already
provide the above SCMI references for the event.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20240325204620.1437237-5-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>