wifi: ath12k: Add fallback for invalid channel number in PHY metadata

wifi: ath12k: Add fallback for invalid channel number in PHY metadata

Currently, ath12k_dp_rx_h_ppdu() determines the band and frequency
based on the channel number and center frequency from the RX descriptor's
PHY metadata. However, in rare cases, it is observed that frequency
retrieved from the metadata may be invalid or unexpected especially for
6 GHz frames.
This can result in a NULL sband, which prevents proper frequency assignment
in rx_status and potentially leading to incorrect RX packet classification.

To fix this potential issue, add a fallback mechanism that uses
ar->rx_channel to populate the band and frequency when the derived
sband is invalid or missing.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1

Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Signed-off-by: Sriram R <quic_srirrama@quicinc.com>
Co-developed-by: Vinith Kumar R <quic_vinithku@quicinc.com>
Signed-off-by: Vinith Kumar R <quic_vinithku@quicinc.com>
Signed-off-by: Aishwarya R <aishwarya.r@oss.qualcomm.com>
Reviewed-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250723190651.699828-1-aishwarya.r@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>