LinuxKPI: 802.11: remove unneeded re-lookup in lkpi_80211_txq_tx_one()

Given we are passed the lsta in as a function argument there is no
need to re-lookup the sta by ni and possibly not find it.
We know the sta and ni from the lsta and whether it is uploaded to
firmware or not we can check directly from the local lsta flag.

MFC after: 3 days
Reviewed by: cc
Differential Revision: https://reviews.freebsd.org/D43965