perf tools: Fix perf usage string leftover

Fixing perf usage string leftover pointed out by Namhyung.
Reported-by: NNamhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-vkcf53oultknsh3ue9fhin94@git.kernel.orgSigned-off-by: NJiri Olsa <jolsa@kernel.org>

tools/perf/perf.c

@@ -18,7 +18,7 @@
 #include <pthread.h>
 
 const char perf_usage_string[] =
-	"perf [--version] [--debug variable[=VALUE]] [--help] COMMAND [ARGS]";
+	"perf [--version] [--help] [OPTIONS] COMMAND [ARGS]";
 
 const char perf_more_info_string[] =
 	"See 'perf help COMMAND' for more information on a specific command.";