watchdog: update email address in conversion doc

The old one is defunct. However, I think it makes sense that I am still
the primary contact person for updates here.
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Link: https://lore.kernel.org/r/20200502143103.19473-1-wsa@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/watchdog/convert_drivers_to_kernel_api.rst

@@ -2,7 +2,7 @@
 Converting old watchdog drivers to the watchdog framework
 =========================================================
 
-by Wolfram Sang <w.sang@pengutronix.de>
+by Wolfram Sang <wsa@kernel.org>
 
 Before the watchdog framework came into the kernel, every driver had to
 implement the API on its own. Now, as the framework factored out the common