ath10k: fix bug in masking of TID value

Although the TID mask is 0xf, the modulus operation does still not
produce identical results as the bitwise and operator. If the TID is 15, the
modulus operation will "convert" it to 0, whereas the bitwise and will keep it
as 15.

This was found during code review.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>