net: airoha: Move ndesc initialization at end of airoha_qdma_init_tx()

In the Linux kernel, the following vulnerability has been resolved:

net: airoha: Move ndesc initialization at end of airoha_qdma_init_tx()

If queue entry list allocation fails in airoha_qdma_init_tx_queue routine,

airoha_qdma_cleanup_tx_queue() will trigger a NULL pointer dereference

accessing the queue entry array. The issue is due to the early ndesc

initialization in airoha_qdma_init_tx_queue(). Fix the issue moving ndesc

initialization at end of airoha_qdma_init_tx routine.