docs: fix broken paths to docs/devel/tracing.txt

With the move of some docs/ to docs/devel/ on ac06724a71,
no references were updated.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/audio/trace-events b/audio/trace-events
index 5173590..1226042 100644
--- a/audio/trace-events
+++ b/audio/trace-events
@@ -1,4 +1,4 @@
-# See docs/tracing.txt for syntax documentation.
+# See docs/devel/tracing.txt for syntax documentation.
 
 # audio/alsaaudio.c
 alsa_revents(int revents) "revents = %d"