Fix hpet_(un)register_irq_handler() for emulation

Fix hpet_(un)register_irq_handler() for when CONFIG_HPET_EMULATE_RTC=n.  They
are provided macros that substitute value 0, but if they are called as
functions and the return value isn't checked, the following warnings appear:

	drivers/char/rtc.c: In function `rtc_init':
	drivers/char/rtc.c:1063: warning: statement with no effect
	drivers/char/rtc.c: In function `rtc_exit':
	drivers/char/rtc.c:1157: warning: statement with no effect
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/rtc.c

@@ -110,8 +110,8 @@ static int rtc_has_irq = 1;
 #define hpet_set_rtc_irq_bit(arg)		0
 #define hpet_rtc_timer_init()			do { } while (0)
 #define hpet_rtc_dropped_irq()			0
-#define hpet_register_irq_handler(h)		0
-#define hpet_unregister_irq_handler(h)		0
+#define hpet_register_irq_handler(h)		({ 0; })
+#define hpet_unregister_irq_handler(h)		({ 0; })
 #ifdef RTC_IRQ
 static irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 {