perf bench: Modify command-list.txt for the entry of perf-bench

This patch modifies command-list.txt for the entry of
perf-bench. So perf will show 'bench' in command list.

Example:
% perf

 usage: perf [--version] [--help] COMMAND [ARGS]

 The most commonly used perf commands are:
   annotate    Read perf.data (created by perf record) and display annotated code
   bench       General framework for benchmark suites
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   list        List all symbolic event types
   probe       Define new dynamic tracepoints
   record      Run a command and record its profile into perf.data
   report      Read perf.data (created by perf record) and display the profile
   sched       Tool to trace/measure scheduler properties (latencies)
   stat        Run a command and gather performance counter statistics
   timechart   Tool to visualize total system behavior during a workload
   top         System profiling tool.
   trace       Read perf.data (created by perf record) and display trace output

 See 'perf help COMMAND' for more information on a specific command.

Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1257853855-28934-4-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>