Fix: Lints

[mberry]

• Removes unnecessary borrows
• Adds parentheses for clarity
• Use subtraction assignment
• Remove unnecessary indexing

[mberry]

So there seems to be an issue with cross compilation and cross-rs in general:

Status: Downloaded newer image for rustembedded/cross:mips64-unknown-linux-gnuabi64-0.1.15
   Compiling libc v0.2.149
   Compiling cfg-if v1.0.0
error[E0463]: can't find crate for `core`
  |
  = note: the `mips64-unknown-linux-gnuabi64` target may not be installed
  = help: consider downloading the target with `rustup target add mips64-unknown-linux-gnuabi64`

error[E0463]: can't find crate for `compiler_builtins`

Was going to leave this open for discussion for a week anyway so hopefully can sort out the CI issues by then.

[tarcieri]

@mberry MIPS was demoted to a Tier 3 target: rust-lang/rust#115218

I would suggest using powerpc-unknown-linux-gnu if you'd like to test against a 32-bit big endian Tier 2 target.

[mberry]

Thanks Tony, that's awesome, would really like to do the full spectrum for quick CI checks in cross.yaml but it's sometimes a moving target.

I'll hopefully try to adjust the scripts later today, Having a BE test is pretty much the important thing here.