perf tools: Remove duplicate const qualifier

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1461577678-29517-1-git-send-email-eric.engestrom@imgtec.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>