irq_work.h: fix warning when CONFIG_IRQ_WORK=n

A randconfig caught repeated compiler warnings when CONFIG_IRQ_WORK=n
due to the definition of a non-inline static function in
<linux/irq_work.h>:

  include/linux/irq_work.h +40 : warning: 'irq_work_needs_cpu' defined but not used

Make it inline to supress the warning.  This is caused commit
00b4295 ("irq_work: Don't stop the tick with pending works") merged
in v3.9-rc1.

Signed-off-by: James Hogan <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/irq_work.h

@@ -37,7 +37,7 @@ void irq_work_sync(struct irq_work *work);
 #ifdef CONFIG_IRQ_WORK
 bool irq_work_needs_cpu(void);
 #else
-static bool irq_work_needs_cpu(void) { return false; }
+static inline bool irq_work_needs_cpu(void) { return false; }
 #endif
 
 #endif /* _LINUX_IRQ_WORK_H */