iwlwifi: mvm: fix TX of CCMP 256

We don't have enough room in the TX command for a CCMP 256
key, and need to use key from table.

Fixes: 3264bf032bd9 ("[BUGFIX] iwlwifi: mvm: Fix CCMP IV setting")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>