Revert "PM / Domains: Handle safely genpd_syscore_switch() call on non-genpd device"

Revert commit 8b55e55ee443 (PM / Domains: Handle safely
genpd_syscore_switch() call on non-genpd device) which was misguided
(the change made by it was not necessary) and it introduced a call to
a function that may sleep into an atomic context code path.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -1148,8 +1148,8 @@ static void genpd_syscore_switch(struct device *dev, bool suspend)
 {
 	struct generic_pm_domain *genpd;
 
-	genpd = genpd_lookup_dev(dev);
-	if (!genpd)
+	genpd = dev_to_genpd(dev);
+	if (!pm_genpd_present(genpd))
 		return;
 
 	if (suspend) {