When station connect to AP of 6 GHz with 40 MHz bandwidth, the TX is
always stay 20 MHz, it is because the flag WMI_PEER_40MHZ is not set
while peer assoc. Add the flag if remote peer is 40 MHz bandwidth.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03003-QCAHSPSWPL_V1_V2_SILICONZ_LITE-2

Fixes: c3a7d7eb ("ath11k: add 6 GHz params in peer assoc command")
Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220119034211.28622-1-quic_wgong@quicinc.com