clocksource: Install completely before selecting

Christian Hoffmann reported that the command line clocksource override
with acpi_pm timer fails:

 Kernel command line: <SNIP> clocksource=acpi_pm
 hpet clockevent registered
 Switching to clocksource hpet
 Override clocksource acpi_pm is not HRT compatible.
 Cannot switch while in HRT/NOHZ mode.

The watchdog code is what enables CLOCK_SOURCE_VALID_FOR_HRES, but we
actually end up selecting the clocksource before we enqueue it into
the watchdog list, so that's why we see the warning and fail to switch
to acpi_pm timer as requested. That's particularly bad when we want to
debug timekeeping related problems in early boot.

Put the selection call last.
Reported-by: Christian Hoffmann <email@christianhoffmann.info>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: stable@kernel.org # 32...
Link: http://lkml.kernel.org/r/%3C1304558210.2943.24.camel%40work-vm%3ESigned-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time/clocksource.c

@@ -685,8 +685,8 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
 	/* Add clocksource to the clcoksource list */
 	mutex_lock(&clocksource_mutex);
 	clocksource_enqueue(cs);
-	clocksource_select();
 	clocksource_enqueue_watchdog(cs);
+	clocksource_select();
 	mutex_unlock(&clocksource_mutex);
 	return 0;
 }
@@ -706,8 +706,8 @@ int clocksource_register(struct clocksource *cs)
 
 	mutex_lock(&clocksource_mutex);
 	clocksource_enqueue(cs);
-	clocksource_select();
 	clocksource_enqueue_watchdog(cs);
+	clocksource_select();
 	mutex_unlock(&clocksource_mutex);
 	return 0;
 }