wifi: wil6210: debugfs: fix info leak in wil_write_file_wmi()

In the Linux kernel, the following vulnerability has been resolved: wifi: wil6210: debugfs: fix info leak in wil_write_file_wmi() The simple_write_to_buffer() function will succeed if even a single byte is initialized. However, we need to initialize the whole buffer to prevent information leaks. Just use memdup_user().