iwlwifi: rs: remove fc variable and other cleanups

This patch
1. Removes use once use only fc variables, they are useless after refactoring
ieee80211 frame control handlers
2. Other trivial cleanups

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>