When HW restart is requested but not started yet, commands would not
be sent to the FW, and some function calls would return an error. In
case of iwl_mvm_mac_sta_state() returning an error value when a
station is removed can lead to an unneeded warning in
__sta_info_destroy_part2().

Handle this by setting the return value to 0, in case HW restart is
in progress.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>