iwlwifi: mvm: clean refs before stop_device()

Some implementations (i.e. mini_rpm) assume the references
are managed only while the device is started.

Move the stale reference cleanup before stopping the
device in order to make them happy.

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