The error being described is for a write operation which is not allowed. In this case, the error is harmless because the the update process is not actually attempting to change the PCIe ASPM policy; it's just encountering this file while traversing the sysfs file system during the update. Since modifying this file is not needed, the error doesn't hold up the update process in any way.
There are kernel parameters and other interventions that can be set up to prevent the error message from appearing, but honestly it's not worth the bother--the simplest thing you can do is just ignore it.