iwlwifi: fix notification wait bug

In "iwlwifi: consolidate the start_device flow"
Emmanuel added the return if the fw isn't there
but forgot to take into account that the struct
for notification wait needs to be added only
after the check -- fix that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>