UPSTREAM: PM: domains: Fix initialization of genpd's next_wakeup

In the genpd governor we walk the list of child-domains to take into
account their next_wakeup. If the child-domain itself, doesn't have a
governor assigned to it, we can end up using the next_wakeup value before
it has been properly initialized. To prevent a possible incorrect behaviour
in the governor, let's initialize next_wakeup to KTIME_MAX.

Bug: 254441685
Fixes: c79aa080 ("PM: domains: use device's next wakeup to determine domain idle state")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit 622d9b55)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I0a8f22c359a01749e61c7be1fdf257f78f9bfdcc