wifi: ath12k: fix possible out-of-bound write in ath12k_wmi_ext_hal_reg_caps()

In the Linux kernel, the following vulnerability has been resolved: wifi: ath12k: fix possible out-of-bound write in ath12k_wmi_ext_hal_reg_caps() reg_cap.phy_id is extracted from WMI event and could be an unexpected value in case some errors happen. As a result out-of-bound write may occur to soc->hal_reg_cap. Fix it by validating reg_cap.phy_id before using it. This is found during code review. Compile tested only.