PM / Sleep: fix async suspend_late/freeze_late error handling

If an asynchronous suspend_late or freeze_late callback fails
during the SUSPEND, FREEZE or QUIESCE phases, we don't propagate the
corresponding error correctly, in effect ignoring the error and
continuing the suspend-to-ram/hibernation. During suspend-to-ram this
could leave some devices without a valid saved context, leading to a
failure to reinitialize them during resume. During hibernation this
could leave some devices active interfeering with the creation /
restoration of the hibernation image. Also this could leave the
corresponding devices without a valid saved context and failure to
reinitialize them during resume.

Fixes: de377b3 (PM / sleep: Asynchronous threads for suspend_late)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Cc: 3.15+ <stable@vger.kernel.org> # 3.15+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/main.c

@@ -1266,6 +1266,8 @@ int dpm_suspend_late(pm_message_t state)
 	}
 	mutex_unlock(&dpm_list_mtx);
 	async_synchronize_full();
+	if (!error)
+		error = async_error;
 	if (error) {
 		suspend_stats.failed_suspend_late++;
 		dpm_save_failed_step(SUSPEND_SUSPEND_LATE);