Change cpu_buffer from array to per_cpu variable in oprofile functions.

[akpm@linux-foundation.org: coding-style fixes]
Cc: Philippe Elie <phil.el@wanadoo.fr>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>