drivers/oprofile: Replace __get_cpu_var uses for address calculation

Replace the uses of __get_cpu_var for address calculation with this_cpu_ptr.

Cc: Robert Richter <rric@kernel.org>
Cc: oprofile-list@lists.sf.net
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>