wifi: ath11k: fix WCN6750 firmware crash caused by 17 num_vdevs

WCN6750 firmware crashes because of num_vdevs changed from 4 to 17
in ath11k_init_wmi_config_qca6390() as the ab->hw_params.num_vdevs
is 17. This is caused by commit f019f4df ("wifi: ath11k: support
2 station interfaces") which assigns ab->hw_params.num_vdevs directly
to config->num_vdevs in ath11k_init_wmi_config_qca6390(), therefore
WCN6750 firmware crashes as it can't support such a big num_vdevs.

Fix it by assign 3 to num_vdevs in hw_params for WCN6750 as 3 is
sufficient too.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3
Tested-on: WCN6750 hw1.0 AHB WLAN.MSL.1.0.1-01371-QCAMSLSWPLZ-1

Fixes: f019f4df

 ("wifi: ath11k: support 2 station interfaces")
Reported-by: Luca Weiss <luca.weiss@fairphone.com>
Tested-by: Luca Weiss <luca.weiss@fairphone.com>
Closes: https://lore.kernel.org/r/D15TIIDIIESY.D1EKKJLZINMA@fairphone.com/
Signed-off-by: Carl Huang <quic_cjhuang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240520030757.2209395-1-quic_cjhuang@quicinc.com