wifi: iwlwifi: mld: clear tzone on fail

wifi: iwlwifi: mld: clear tzone on fail

iwl_mld_thermal_zone_register() stores the thermal zone pointer in
mld->tzone before calling thermal_zone_device_enable(). If enable
fails, the code unregisters the zone but leaves mld->tzone stale,
so iwl_mld_thermal_zone_unregister() can unregister it again.
Clear mld->tzone after unregister in the error path.

While at it remove a pointless if in iwl_mld_thermal_zone_unregister
after we've alredy checked the tzone pointer is not NULL.

Assisted-by: GitHubCopilot:gpt-5.3-codex
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://patch.msgid.link/20260714141909.595dcb8cb7fe.I8125e4a2eeb0390798e3f4074c62c00443eda8e8@changeid
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>