trivial: ftrace:fix description of trace directory

Fix trace source directory from kernel/tracing/ to kernel/trace/.

Signed-off-by: GeunSik Lim <geunsik.lim@samsung.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 2a82d86..7bd27f0 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -1834,4 +1834,4 @@
 -----------
 
 More details can be found in the source code, in the
-kernel/tracing/*.c files.
+kernel/trace/*.c files.