watchdog: Make watchdog_class const

Now that the driver core allows for struct class to be in read-only
memory, mark watchdog_class as const.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/watchdog_dev.c

···
 	.fops		= &watchdog_fops,
 };
 
-static struct class watchdog_class = {
+static const struct class watchdog_class = {
 	.name =		"watchdog",
 	.dev_groups =	wdt_groups,
 };