ath9k/htc_drv_main: off by one error

I changed "> ATH9K_HTC_MAX_TID" to ">= ATH9K_HTC_MAX_TID" to avoid a
potential overflow.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>