Clippy fix

I fixed some things that clippy is not happy about either. Mainly I removed redundant code like.

There are at least 2 things left like:

• Rewriting if chain with match in mount.rs.
  I don't really know how one would move that to a match unless one uses ranges like 1..isize::MAX => {...}.
• Handling the read amount in mount.rs with Read::read_exact. According to clippy it's more of an error than just a warning.
  I am unsure whether to "fix" this as I am not too familiar with the surrounding code. It looks okay to me to change it however.