iwlwifi: tid_data is taken twice in iwl_trans_pcie_tx_agg_alloc

Remove this redundancy.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>