firmware-<qcom-msm8916>: adjust for new venus firmware path (MR 4553)

Linux 6.7-rc1 looks for the venus (video) firmware in
qcom/venus-1.8/venus.mbn instead of qcom/venus-1.8/venus.mdt.

Let's install it in both places with a symlink so that the firmware
packages work for both older and newer Linux versions.

[ci:ignore-count]: lots of packages
[ci:skip-build] already built successfully in CI