alarmtimer: Make alarmtimer_get_rtcdev() a stub when CONFIG_RTC_CLASS=n

The stubbed version of alarmtimer_get_rtcdev() is not exported.
so this won't work if this function is used in a module when
CONFIG_RTC_CLASS=n.

Move the stub function to the header file and make it inline so that
callers don't have to worry about linking against this symbol.

rtcdev isn't used outside of this ifdef so it's not required to be
redefined to NULL. Drop that while touching this area.
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200124055849.154411-4-swboyd@chromium.org

include/linux/alarmtimer.h

@@ -60,7 +60,11 @@ u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval);
 u64 alarm_forward_now(struct alarm *alarm, ktime_t interval);
 ktime_t alarm_expires_remaining(const struct alarm *alarm);
 
+#ifdef CONFIG_RTC_CLASS
 /* Provide way to access the rtc device being used by alarmtimers */
 struct rtc_device *alarmtimer_get_rtcdev(void);
+#else
+static inline struct rtc_device *alarmtimer_get_rtcdev(void) { return NULL; }
+#endif
 
 #endif

kernel/time/alarmtimer.c

@@ -143,11 +143,6 @@ static void alarmtimer_rtc_interface_remove(void)
 	class_interface_unregister(&alarmtimer_rtc_interface);
 }
 #else
-struct rtc_device *alarmtimer_get_rtcdev(void)
-{
-	return NULL;
-}
-#define rtcdev (NULL)
 static inline int alarmtimer_rtc_interface_setup(void) { return 0; }
 static inline void alarmtimer_rtc_interface_remove(void) { }
 static inline void alarmtimer_rtc_timer_init(void) { }