perf tools: Fix the bash completion for listing subsubcommands of perf subcommand

perf tools: Fix the bash completion for listing subsubcommands of perf subcommand

The bash completion does not support listing subsubcommands for 'perf
kvm|kmem|mem|lock|sched --<long option> <TAB>', where 'kvm|kmem|mem|
lock|sched' are all subcommands of perf.

Example:

Before this patch:

 $ perf kvm --verbose <TAB>
 $

As shown above, the subsubcommands of perf kvm does not come out.

After this patch:

 $ perf kvm --verbose <TAB>
 buildid-list  diff          record        report        stat
 top

As shown above, the subsubcommands of perf kvm can come out now.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1426685758-25488-3-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>