genirq: Fix UP compile failure caused by irq_thread_check_affinity

Since genirq: Delegate irq affinity setting to the irq thread
(591d2fb0) compilation with
CONFIG_SMP=n fails with following error:

/usr/src/linux-2.6/kernel/irq/manage.c:
   In function 'irq_thread_check_affinity':
/usr/src/linux-2.6/kernel/irq/manage.c:475:
   error: 'struct irq_desc' has no member named 'affinity'
make[4]: *** [kernel/irq/manage.o] Error 1

That commit adds a new function irq_thread_check_affinity() which
uses struct irq_desc.affinity which is only available for CONFIG_SMP=y.
Move that function under #ifdef CONFIG_SMP.

[ tglx@brownpaperbag: compile and boot tested on UP and SMP ]
Signed-off-by: Bruno Premont <bonbons@linux-vserver.org>
LKML-Reference: <20090722222232.2eb3e1c4@neptune.home>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/manage.c

@@ -451,6 +451,7 @@ static int irq_wait_for_interrupt(struct irqaction *action)
 	return -1;
 }
 
+#ifdef CONFIG_SMP
 /*
  * Check whether we need to change the affinity of the interrupt thread.
  */
@@ -478,6 +479,10 @@ irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action)
 	set_cpus_allowed_ptr(current, mask);
 	free_cpumask_var(mask);
 }
+#else
+static inline void
+irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action) { }
+#endif
 
 /*
  * Interrupt handler thread