iwlwifi: make iwl_txq_dyn_alloc_dma() return the txq

Use the ERR_PTR() machinery to return the queue or an
error, instead of having a separate out parameter.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220210181930.1f0c5d72fb89.Iefca56d535558b7a8d23204fd16129c17b6704b6@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>