[S390] fix build breakage with CONFIG_AIO=n

next-20090925 randconfig build breaks on s390x, with CONFIG_AIO=n.

arch/s390/mm/pgtable.c: In function 's390_enable_sie':
arch/s390/mm/pgtable.c:282: error: 'struct mm_struct' has no member named 'ioctx_list'
arch/s390/mm/pgtable.c:298: error: 'struct mm_struct' has no member named 'ioctx_list'
make[1]: *** [arch/s390/mm/pgtable.o] Error 1

Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -279,7 +279,10 @@ int s390_enable_sie(void)
 	/* lets check if we are allowed to replace the mm */
 	task_lock(tsk);
 	if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
-	    tsk->mm != tsk->active_mm || !hlist_empty(&tsk->mm->ioctx_list)) {
+#ifdef CONFIG_AIO
+	    !hlist_empty(&tsk->mm->ioctx_list) ||
+#endif
+	    tsk->mm != tsk->active_mm) {
 		task_unlock(tsk);
 		return -EINVAL;
 	}
@@ -295,7 +298,10 @@ int s390_enable_sie(void)
 	/* Now lets check again if something happened */
 	task_lock(tsk);
 	if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
-	    tsk->mm != tsk->active_mm || !hlist_empty(&tsk->mm->ioctx_list)) {
+#ifdef CONFIG_AIO
+	    !hlist_empty(&tsk->mm->ioctx_list) ||
+#endif
+	    tsk->mm != tsk->active_mm) {
 		mmput(mm);
 		task_unlock(tsk);
 		return -EINVAL;