iwlwifi: mvm: clear IN_HW_RESTART flag on stop()

On stop(), we already cleared our internal state,
and the restart_complete() callback won't be
called, so simply clear the IN_HW_RESTART flag.

Keeping the flag might result in invalid state
on the next start(), preventing the driver starting
properly.

Additionally, don't take IWL_MVM_REF_UCODE_DOWN on stop()
if hw restart was requested, as the ref was already
taken in this case.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>