OPP: Allow notifiers to call dev_pm_opp_get_{voltage, freq} RCU-free

We pass the dev_pm_opp structure to OPP notifiers but the users
of the notifier need to surround calls to dev_pm_opp_get_*() with
RCU read locks to avoid lockdep warnings. The notifier is already
called with the dev_opp's srcu lock held, so it should be safe to
assume the devm_pm_opp structure is already protected inside the
notifier. Update the lockdep check for this.

Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>