driver core: constify devlink class

The devlink class object is never modified and can be made constant.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20241014122849.118766-1-brgl@bgdev.pl


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>