watchdog: diag288_wdt: Remove leftover includes from conversion to watchdog API

Commit f7a94db4 ("s390/watchdog: use watchdog API") converted
the driver to use the watchdog API, but some includes as well as
MODULE_ALIAS_MISCDEV() were missed.

Cc: Philipp Hachtmann <phacht@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>