PM / Domains: Fix unsafe iteration over modified list of domain providers

commit b556b15dc04e9b9b98790f04c21acf5e24f994b2 upstream.

of_genpd_del_provider() iterates over list of domain provides and
removes matching element thus it has to use safe version of list
iteration.

Fixes: aa42240a (PM / Domains: Add generic OF-based PM domain look-up)
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>