iwlwifi: remove an unused argument

The station ID argument to the function
iwlagn_tx_cmd_build_hwcrypto isn't used
so remove it.

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>