devlink: add missing unregister linecard notification

Cited fixes commit introduced linecard notifications for register,
however it didn't add them for unregister. Fix that by adding them.

Fixes: c246f9b5

 ("devlink: add support to create line card and expose to user")
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230817125240.2144794-1-jiri@resnulli.us
Signed-off-by: Jakub Kicinski <kuba@kernel.org>