perf/scripts: Fix supported language listing option

'perf trace -s list' prints a list of the supported scripting
languages.  One problem with it is that it falls through and prints
the trace as well.  The use of 'list' for this also makes it easy to
confuse with 'perf trace -l', used for listing available scripts.  So
change 'perf trace -s list' to 'perf trace -s lang' and fixes the
fall-through problem.

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Keiichi KII <k-keiichi@bx.jp.nec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1264580883-15324-2-git-send-email-tzanussi@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>