s390/watchdog: enable KEEPALIVE for /dev/watchdog

There's no reason why we wouldn't want to be able to send a keep alive
message to /dev/watchdog (feed dog) for the s390 diag288 watchdog, so
let's enable the WDIOF_KEEPALIVEPING option.

Signed-off-by: Xu Wang <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/watchdog/diag288_wdt.c

···
 };
 
 static struct watchdog_info wdt_info = {
-	.options = WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE,
+	.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
 	.firmware_version = 0,
 	.identity = "z Watchdog",
 };