Fix links in Watchdog.md

Fix broken links, so docs build.

Author: AnotherButler

docs/porting/target/Watchdog.md

@@ -28,9 +28,9 @@ Hardware Independent Watchdog support.
 
 ## Implementing Watchdog
 
-You can find the API and specification for the Watchdog API in the following header file:
+You can find the API and specification for the Watchdog API in its HAL API reference:
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/feature-hal-spec-watchdog-doxy/classmbed_1_1_watchdog.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/mbed-os/development/mbed-os-api-doxy/group__hal__watchdog.html)
 
 To enable Watchdog support in Mbed OS, add the `WATCHDOG` label in the `device_has` option of the target's section in the `targets.json` file.
 
@@ -42,8 +42,6 @@ The Mbed OS HAL provides a set of conformance tests for Watchdog. You can use th
 mbed test -t <toolchain> -m <target> -n "tests-mbed_hal-watchdog*"
 ```
 
-You can read more about the test cases here:
+For more details, please see:
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/feature-hal-spec-watchdog-doxy/watchdog__api__tests_8h_source.html)
-
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/feature-hal-spec-watchdog-doxy/watchdog__reset__tests_8h_source.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/mbed-os/development/mbed-os-api-doxy/group__hal__watchdog__tests.html)