PM: check sysdev_suspend(PMSG_FREEZE) return value

Check the return value of sysdev_suspend().  I think this was a typo.
Without this change, the following "if" check is always false.
I also changed the error message so it's distinguishable from the
similar message a few lines above.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

kernel/power/disk.c

@@ -241,9 +241,9 @@ static int create_image(int platform_mode)
 
 	local_irq_disable();
 
-	sysdev_suspend(PMSG_FREEZE);
+	error = sysdev_suspend(PMSG_FREEZE);
 	if (error) {
-		printk(KERN_ERR "PM: Some devices failed to power down, "
+		printk(KERN_ERR "PM: Some system devices failed to power down, "
 			"aborting hibernation\n");
 		goto Enable_irqs;
 	}