1. register_wide_hw_breakpoint() can use unregister_ if failure,
   no need to duplicate the code.

2. "struct perf_event **pevent" adds the unnecesary lever of
   indirection and complication, use per_cpu(*cpu_events, cpu).
Reported-by: NVince Weaver <vincent.weaver@maine.edu>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20130620155018.GA6347@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>