iwlwifi: pcie: keep trans instead of trans_pcie in iwl_txq

We used both the trans and the trans_pcie structures in
iwl_txq, so we can keep the trans structure instead.  This
helps with the refactoring of txq code out of pcie.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200529092401.1f826d34339e.I23182a59bfbe089a1f659742d6fee6f64d2ed08c@changeid