windows: fix fio_cpu_count() definition

Don't take a 'cpu' argument, that's a leftover when this was
(temporarily) fio_cpu_isset().

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/os/os-windows.h b/os/os-windows.h
index d465818..243edc6 100644
--- a/os/os-windows.h
+++ b/os/os-windows.h
@@ -215,7 +215,7 @@
 	*mask |= 1 << cpu;
 }
 
-static inline int fio_cpu_count(os_cpu_mask_t *mask, int cpu)
+static inline int fio_cpu_count(os_cpu_mask_t *mask)
 {
 	return hweight64(*mask);
 }