wifi: ath12k: avoid redundant code in Rx cookie conversion init

Currently, in the Rx data path cookie conversion initialization procedure,
the primary page table index (ppt_idx) is computed within the secondary
page table iteration. However this is invariant, and hence the ppt_idx
should be calculated outside of the iteration to avoid repeated execution
of the statement.

Found in code review.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.1.1-00188-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240411102226.4045323-2-quic_periyasa@quicinc.com