[MIPS] AU1xxx mips_timer_interrupt() fixes

common/au1000/irq.c was missing a mips_timer_interrupt() prototype,
whereas in common/au1000/time.c the actual mips_timer_interrupt()
implementation was missing an irq_exit() invocation, causing a
preempt_count() leak.
    
Signed-off-by: Herbert Valerio Riedel <hvr@hvrlab.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/au1000/common/irq.c

@@ -68,6 +68,7 @@
 
 extern void set_debug_traps(void);
 extern irq_cpustat_t irq_stat [NR_CPUS];
+extern void mips_timer_interrupt(struct pt_regs *regs);
 
 static void setup_local_irq(unsigned int irq, int type, int int_req);
 static unsigned int startup_irq(unsigned int irq);

arch/mips/au1000/common/time.c

@@ -116,6 +116,7 @@ void mips_timer_interrupt(struct pt_regs *regs)
 
 null:
 	ack_r4ktimer(0);
+	irq_exit();
 }
 
 #ifdef CONFIG_PM