[S390] Fix init irq proc build break.

Embed init_irq_proc(s390) within CONFIG_PROC_FS to fix a build break.

Signed-off-by : Sachin Sant <sachinp@in.ibm.com>

arch/s390/kernel/irq.c

@@ -95,6 +95,7 @@ asmlinkage void do_softirq(void)
 	local_irq_restore(flags);
 }
 
+#ifdef CONFIG_PROC_FS
 void init_irq_proc(void)
 {
 	struct proc_dir_entry *root_irq_dir;
@@ -102,3 +103,4 @@ void init_irq_proc(void)
 	root_irq_dir = proc_mkdir("irq", NULL);
 	create_prof_cpu_mask(root_irq_dir);
 }
+#endif