clocksource: Implement clocksource_select_fallback() for CONFIG_ARCH_USES_GETTIMEOFFSET=y

commit 7eaeb343 (clocksource: Provide unbind interface in sysfs)
implemented clocksource_select_fallback() which is not defined for
CONFIG_ARCH_USES_GETTIMEOFFSET=y. Add an empty inline function for
that.
Reported-by: NIngo Molnar <mingo@kernel.org>
Reported-by: fengguang.wu@intel.com
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

kernel/time/clocksource.c

@@ -632,6 +632,7 @@ static void clocksource_select_fallback(void)
 #else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
 
 static inline void clocksource_select(void) { }
+static inline void clocksource_select_fallback(void) { }
 
 #endif