[Fix] `nvm which`: show alias name in infinite loop error message

`${2}` was empty because positional parameters had been consumed by `shift` in the argument parsing loop.
Use `${provided_version}` which holds the resolved alias name.

Bug introduced in https://github.com/nvm-sh/nvm/commit/1c00753fd9c3ae5e0bb3f4992c5e283ef5bf5085.