drm/amd/display: Avoid HDCP over-read and corruption

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Avoid HDCP over-read and corruption Instead of reading the desired 5 bytes of the actual target field, the code was reading 8. This could result in a corrupted value if the trailing 3 bytes were non-zero, so instead use an appropriately sized and zero-initialized bounce buffer, and read only 5 bytes before casting to u64.