wifi: ath11k: fix wrong overriding for VHT Beamformee STS Capability

wifi: ath11k: fix wrong overriding for VHT Beamformee STS Capability

Current code in ath11k_mac_set_txbf_conf overrides nsts, which is
incorrect as it confuses nss and nsts. nss is Number of Spatial
Streams，nsts is Number of Space-Time Streams.

As mentioned in Fixes: 55b5ee3357d7, the nss used when acting as a
beamformee in VHT mode should be reported by the firmware and should not
be greater than the number of receiving antennas - 1. The num_rx_chains
related nss rather than nsts.

If STBC is enabled, nsts is greater than nss. About nss are mapped to
nsts, refer to IEEE Std 802.11-2020: 19.3.11.9.2 Space-time block coding
(STBC), Table 19-18—Constellation mapper output to spatial mapper input
for STBC.

Remove wrong overriding for nsts of VHT Beamformee STS Capability,
acting DL MU-MIMO in VHT mode is working properly.

Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-04479-QCAHSPSWPL_V1_V2_SILICONZ_IOE-1

Fixes: 55b5ee3357d7 ("wifi: ath11k: fix number of VHT beamformee spatial streams")
Signed-off-by: Yu Zhang (Yuriy) <quic_yuzha@quicinc.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250124075953.2282354-1-quic_yuzha@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>