qcacld-3.0: Remove use-after-free of frame in tx mgmt send

The tx completion handler for the frame frees the buffer.
Therefore, usage of frame after tx completion causes undesired
effect.

Remove the dereference of tx frame buffer contents in
lim_tx_mgmt_frame() after the tx completion.

Change-Id: I32211e1bce4f96ba920a2212ef65aa39831666ab
CRs-Fixed: 3772014