PM-runtime: Fix autosuspend_delay on 32bits arch

Cast autosuspend_delay to u64 to make sure that the full computation
of 'expires' or slack will be done in u64, even on 32bits arch.

Otherwise, any delay greater than 2^31 nsec can overflow if signed
32bits is used when converting delay from msec to nsec.

Fixes: 8234f673 (PM-runtime: Switch autosuspend over to using hrtimers)
Reported-by: Tony Lindgren <tony@atomide.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/runtime.c

@@ -141,7 +141,7 @@ u64 pm_runtime_autosuspend_expiration(struct device *dev)
 
 	last_busy = READ_ONCE(dev->power.last_busy);
 
-	expires = last_busy + autosuspend_delay * NSEC_PER_MSEC;
+	expires = last_busy + (u64)autosuspend_delay * NSEC_PER_MSEC;
 	if (expires <= now)
 		expires = 0;	/* Already expired. */
 
@@ -525,7 +525,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 				 * We add a slack of 25% to gather wakeups
 				 * without sacrificing the granularity.
 				 */
-				u64 slack = READ_ONCE(dev->power.autosuspend_delay) *
+				u64 slack = (u64)READ_ONCE(dev->power.autosuspend_delay) *
 						    (NSEC_PER_MSEC >> 2);
 
 				dev->power.timer_expires = expires;