The functions used during NUMA initialization - *_numa_init() and
*_scan_nodes() - have different arguments and return values.  Unify
them such that they all take no argument and return 0 on success and
-errno on failure.  This is in preparation for further NUMA init
cleanups.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Shaohui Zheng <shaohui.zheng@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: H. Peter Anvin <hpa@linux.intel.com>