wifi: ath12k: Use scan link ID 15 for all scan operations

wifi: ath12k: Use scan link ID 15 for all scan operations

According to the code documentation in ath12k_mac_op_hw_scan(), "if no
links of an ML VIF are already active on the radio corresponding to the
given scan frequency, the scan link (link ID 15) should be used". This rule
should apply to non-ML interfaces as well to maintain uniformity across the
driver. However, currently, link 0 is selected as the scan link during
non-ML operations.

Update the code to use scan link ID 15 in all cases.

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

Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Signed-off-by: Aditya Kumar Singh <aditya.kumar.singh@oss.qualcomm.com>
Link: https://patch.msgid.link/20250417-fix_scan_vdev_handling-v3-2-9ec42513d26b@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>