Documentation: fix selftests related file refs

Make refs to selftests files valid including:
  - watchdog-test.c
  - dnotify_test.c

Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/watchdog/pcwd-watchdog.txt b/Documentation/watchdog/pcwd-watchdog.txt
index 4f68052..b8e60a4 100644
--- a/Documentation/watchdog/pcwd-watchdog.txt
+++ b/Documentation/watchdog/pcwd-watchdog.txt
@@ -25,7 +25,7 @@
 
  If you want to write a program to be compatible with the PC Watchdog
  driver, simply use of modify the watchdog test program:
- Documentation/watchdog/src/watchdog-test.c
+ tools/testing/selftests/watchdog/watchdog-test.c
 
 
  Other IOCTL functions include: