iwlwifi: mvm: update ucode status before stopping device

Leaving ucode_loaded to true after stop_device() has been called
is a recipe for problems. Flows that are not sync'ed with the
driver life cycle (like debugfs hooks and thermal hooks) must
check that the firmware is loaded before they interact with it.
Therefore we need to keep this variable updated with the real
status of the firmware.

Signed-off-by: Chaya Rachel Ivgi <chaya.rachel.ivgi@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>