x86, mce: trivial clean up for mce_intel_64.c

Fix for:

WARNING: space prohibited between function name and open parenthesis '('
+       for_each_online_cpu (cpu) {

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>