Update functions.sh

For some reason the check did not work as expected. (possilby because I forgot to negate the second condition. It should only exit if x86 was found but not the qemu-aarch64-static binary. Rewritten to use a if then fi block to ensure the error message is only thrown if the combined expression evaluates to true

I goofed the architecture check and the binary check 🤦

https://forum.manjaro.org/t/issue-during-build-image-process-after-manjaro-arm-tools-update/166851