wifi: rtw88: Add NULL check for chip->edcca_th in rtw_fw_adaptivity_result()

In the Linux kernel, the following vulnerability has been resolved: wifi: rtw88: Add NULL check for chip->edcca_th in rtw_fw_adaptivity_result() It was recently reported that rtw_fw_adaptivity_result() in fw.c dereferences rtwdev->chip->edcca_th without a NULL check. The issue is that devices with the 8821CE chip don't define edcca_th in their chip info. As a result, when rtw_fw_adaptivity_result() tries to dereference it, the kernel triggers an oops. Add a NULL check for edcca_th before dereferencing it in rtw_fw_adaptivity_result() in fw.c. Placing the check at the function entry avoids logging any garbage values. This change does not address the root cause for this behavior, but it prevents the NULL dereference and the resulting oops while a more permanent solution is developed. Tested on a 8822CE chip which defines edcca_th, so this issue is not present on it, but it still uses this driver and I can verify there are no regressions.