ath5k: remove now unused variable declared in ath5k_tx

  CC [M]  drivers/net/wireless/ath5k/base.o
drivers/net/wireless/ath5k/base.c: In function ‘ath5k_tx’:
drivers/net/wireless/ath5k/base.c:2598: warning: unused variable ‘info’

Signed-off-by: John W. Linville <linville@tuxdriver.com>