net: hns3: fix double free issue for tx spare buffer

In the Linux kernel, the following vulnerability has been resolved: net: hns3: fix double free issue for tx spare buffer In hns3_set_ringparam(), a temporary copy (tmp_rings) of the ring structure is created for rollback. However, the tx_spare pointer in the original ring handle is incorrectly left pointing to the old backup memory. Later, if memory allocation fails in hns3_init_all_ring() during the setup, the error path attempts to free all newly allocated rings. Since tx_spare contains a stale (non-NULL) pointer from the backup, it is mistaken for a newly allocated buffer and is erroneously freed, leading to a double-free of the backup memory. The root cause is that the tx_spare field was not cleared after its value was saved in tmp_rings, leaving a dangling pointer. Fix this by setting tx_spare to NULL in the original ring structure when the creation of the new `tx_spare` fails. This ensures the error cleanup path only frees genuinely newly allocated buffers.