rtc: remove and clarify unneeded externs

When CONFIG_HPET_EMULATE_RTC is defined the external declaration of
hpet_rtc_interrupt is redundant due to the inclusion of hpet.h.

When !CONFIG_HPET_EMULATE_RTC we make it clear that hpet_rtc_interrupt is
not used by defining it to return zero.
Signed-off-by: NCarlos R. Mafra <crmafra@ift.unesp.br>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/rtc.c

@@ -121,8 +121,6 @@ static irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 	return 0;
 }
 #endif
-#else
-extern irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id);
 #endif
 
 /*

drivers/rtc/rtc-cmos.c

@@ -52,7 +52,10 @@
 #define hpet_rtc_timer_init() 			do { } while (0)
 #define hpet_register_irq_handler(h) 		0
 #define hpet_unregister_irq_handler(h)		do { } while (0)
-extern irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id);
+static irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
+{
+	return 0;
+}
 #endif
 
 struct cmos_rtc {