No need to disable preemption in the debug_atomic_* ops, as
we ensure interrupts are disabled already.

So let's use the __this_cpu_ops() rather than this_cpu_ops() that
enclose the ops in a preempt disabled section.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>