platform/mellanox: Remove unnecessary code

Remove redundant 'NULL' check for of if 'data->notifier'.

Replace 'return err' by 'return 0' in mlxreg_lc_probe().

Fixes: 62f9529b ("platform/mellanox: mlxreg-lc: Add initial support for Nvidia line card devices")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20220823201937.46855-4-vadimp@nvidia.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>