x86: Use online node real index in calulate_tbl_offset()

Found a NUMA system that doesn't have RAM installed at the first
socket which hangs while executing init scripts.

bisected it to:

 | commit 93296720
 | Author: Shaohua Li <shaohua.li@intel.com>
 | Date:   Wed Oct 20 11:07:03 2010 +0800
 |
 |     x86: Spread tlb flush vector between nodes

It turns out when first socket is not online it could have cpus on
node1 tlb_offset set to bigger than NUM_INVALIDATE_TLB_VECTORS.

That could affect systems like 4 sockets, but socket 2 doesn't
have installed, sockets 3 will get too big tlb_offset.

Need to use real online node idx.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Shaohua Li <shaohua.li@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4CDEDE59.40603@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>