mlxsw: core_thermal: Remove unnecessary checks

mlxsw_thermal_module_fini() cannot be invoked with a thermal module
which is NULL or which is not associated with a thermal zone, so remove
these checks.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Link: https://patch.msgid.link/8db5fe0a3a28ba09a15d4102cc03f7e8ca7675be.1722345311.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>