MIPS: idle: Add prototype for function check_wait

This commit adds a prototype to fix warning at W=1:

  arch/mips/kernel/idle.c:126:13: error: no previous prototype for 'check_wait' [-Werror=missing-prototypes]
Signed-off-by: Pujin Shi <shipujin.t@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/idle.h

@@ -15,6 +15,8 @@ static inline int using_rollback_handler(void)
 	return cpu_wait == r4k_wait;
 }
 
+extern void __init check_wait(void);
+
 extern int mips_cpuidle_wait_enter(struct cpuidle_device *dev,
 				   struct cpuidle_driver *drv, int index);