uv: Replace __get_cpu_var

Use __this_cpu_read instead.

Cc: Hedi Berriche <hedi@sgi.com>
Cc: Mike Travis <travis@sgi.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>