qcacld-3.0: Fix memory leak issue

Object 'tx_conf_event' was dereferenced after being freed by calling
'qdf_mem_free(tx_conf_event)' function. Object 'tx_conf_event->nbuf'
can't be freed.

Free 'tx_conf_event->buf' before 'tx_conf_event' free.

Change-Id: Id5a8f17db4d58395837db9878c6c7d87e9fe40c4
CRs-Fixed: 2503761
1 file changed