wifi: ath12k: fix ATH12K_FLAG_REGISTERED flag handling

wifi: ath12k: fix ATH12K_FLAG_REGISTERED flag handling

Commit a5686ae820fa ("wifi: ath12k: move ATH12K_FLAG_REGISTERED handling to
ath12k_mac_register()") relocated the setting of the ATH12K_FLAG_REGISTERED
flag to the ath12k_mac_register() function. However, this function only
accesses the first device (ab) via ag->ab[0], resulting in the flag being
set only for the first device in the group. Similarly,
ath12k_mac_unregister() only unsets the flag for the first device. The flag
should actually be set for all devices in the group to avoid issues during
recovery.

Hence, move setting and clearing of this flag in the function
ath12k_core_hw_group_start() and ath12k_core_hw_group_stop() respectively.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: a5686ae820fa ("wifi: ath12k: move ATH12K_FLAG_REGISTERED handling to ath12k_mac_register()")
Signed-off-by: Aditya Kumar Singh <aditya.kumar.singh@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250408-fix_reboot_issues_with_hw_grouping-v4-4-95e7bf048595@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>