aio: fix kioctx leak introduced by "aio: Fix a trinity splat"

e34ecee2 reworked the percpu reference
counting to correct a bug trinity found.  Unfortunately, the change lead
to kioctxes being leaked because there was no final reference count to
put.  Add that reference count back in to fix things.
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Cc: stable@vger.kernel.org

fs/aio.c

@@ -653,6 +653,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
 	spin_unlock(&aio_nr_lock);
 
 	percpu_ref_get(&ctx->users);	/* io_setup() will drop this ref */
+	percpu_ref_get(&ctx->reqs);	/* free_ioctx_users() will drop this */
 
 	err = ioctx_add_table(ctx, mm);
 	if (err)