ath10k: fix compile time sanity check for CE4 buffer size

In 'ath10k_ce_alloc_pipe' the compile time sanity check to
ensure that there is sufficient buffers in CE4 for HTT Tx
MSDU descriptors, but this did not take into account of the
case with 'peer flow control' enabled, fix this.

Cc: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>