ath10k: fix HTT Tx CE ring size

QCA4019 can queue up to 2500 frames at a time.
This means it requires roughly 5000 entires on the
ring to work properly. Otherwise random tx failure
may occur.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>