mac80211: tx: delete a redundant if statement in ieee80211_check_fast_xmit()

If statement is meaningless because the code will goto out regardless of
whether fast_tx is NULL or not.

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Link: https://lore.kernel.org/r/20220413091902.27438-1-hbh25y@gmail.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>