docs: watchdog: Fix build error.

make htmldocs fails due to missing blank line following header.

Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>