ath9k: fix oops on trying to hold the wrong spinlock

We were trying to hold the wrong spinlock due to a typo
on IEEE80211_BAR_CTL_TID_S's definition. We use this to
compute the tid number and then hold this this tid number's
spinlock.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>