hw_breakpoint: Simplify *register_wide_hw_breakpoint()

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: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20130620155018.GA6347@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>