iwlwifi: remove STATUS_MODE_PENDING

Since rfkill integration, mac80211 can no
longer add an interface while the hardware
is not ready, so STATUS_MODE_PENDING can
never be set.

Also, remove another superfluous channel
sanity check and return the commit_rxon
return value in case it failed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>