iwlwifi: pcie: fix recovery from ARC reset in WoWLAN

When the ARC is reset when we exit from Sx in case we had
WoWLAN running, we can't access the prph before we reset
the NIC.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>