Resolve inconsistent_struct_constructor style lint
Resolve inconsistent_struct_constructor style lint

    error: inconsistent struct constructor
        --> src/item.rs:1497:16
         |
    1497 |               Ok(Signature {
         |  ________________^
    1498 | |                 constness,
    1499 | |                 asyncness,
    1500 | |                 unsafety,
    ...    |
    1508 | |                 generics,
    1509 | |             })
         | |_____________^ help: try: `Signature { constness, asyncness, unsafety, abi, fn_token, ident, generics, paren_token, inputs, variadic, output }`
         |
         = note: `-D clippy::inconsistent-struct-constructor` implied by `-D clippy::all`
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#inconsistent_struct_constructor

dtolnay/syn