Fixes adjustment of max_width within macros

[csmulhern]

Fixes #5404.

Minimal example:

macro_rules! foo {
    () => {
        println!("Hello, world!");
    };
}

Without this change:

> cargo run --bin rustfmt -- --config-path=/dev/null --config=max_width=100 --config=fn_call_width=100 ~/Desktop/example.rs
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/rustfmt --config-path=/dev/null --config=max_width=100 --config=fn_call_width=100 /Users/cameron/Desktop/example.rs`
`fn_call_width` cannot have a value that exceeds `max_width`. `fn_call_width` will be set to the same value as `max_width`

With this change:

> cargo run --bin rustfmt -- --config-path=/dev/null --config=max_width=100 --config=fn_call_width=100 ~/Desktop/example.rs
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s
     Running `target/debug/rustfmt --config-path=/dev/null --config=max_width=100 --config=fn_call_width=100 /Users/cameron/Desktop/example.rs`