x86/oprofile: fix on_each_cpu build error

Signed-off-by: Robert Richter <robert.richter@amd.com>
Cc: oprofile-list <oprofile-list@lists.sourceforge.net>
Cc: Jason Yeh <jason.yeh@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>