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/hpwdt.txt b/Documentation/watchdog/hpwdt.txt
index 7a9f635..6d866c5 100644
--- a/Documentation/watchdog/hpwdt.txt
+++ b/Documentation/watchdog/hpwdt.txt
@@ -15,7 +15,7 @@
 
  Watchdog functionality is enabled like any other common watchdog driver. That
  is, an application needs to be started that kicks off the watchdog timer. A
- basic application exists in the Documentation/watchdog/src directory called
+ basic application exists in tools/testing/selftests/watchdog/ named
  watchdog-test.c. Simply compile the C file and kick it off. If the system
  gets into a bad state and hangs, the HPE ProLiant iLO timer register will
  not be updated in a timely fashion and a hardware system reset (also known as