wifi: ath12k: fix signal in radiotap for WCN7850

wifi: ath12k: fix signal in radiotap for WCN7850

Currently host will add ATH12K_DEFAULT_NOISE_FLOOR to rssi_comb to
convert RSSI from dB to dBm.

For WCN7850, this conversion is unnecessary because the RSSI value is
already reported in dBm units.

No longer convert for those firmware that already support dBM conversion.

This patch won't affect QCN chips.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Signed-off-by: Kang Yang <kang.yang@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/20250722095934.67-2-kang.yang@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>