perf kmem: Print usage help for unknown commands

This patch fixes "perf kmem" to print usage help instead of
doing nothing.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
LKML-Reference: <1263921971-10782-1-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/builtin-kmem.c

@@ -784,7 +784,8 @@ int cmd_kmem(int argc, const char **argv, const char *prefix __used)
 			setup_sorting(&alloc_sort, default_sort_order);
 
 		return __cmd_kmem();
-	}
+	} else
+		usage_with_options(kmem_usage, kmem_options);
 
 	return 0;
 }