iwlwifi: release IRQ in error path

smatch correctly complains:
iwl-trans-pcie.c +1528 iwl_trans_pcie_start_hw(50) warn: 'trans->irq' was not released on error

Fix it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi W Guy <wey-yi.w.guy@intel.com>