Resolve needless_return clippy lint in PR 2553

    warning: unneeded `return` statement
        --> serde_derive/src/de.rs:2986:13
         |
    2986 |             return quote!(#assign_to __default.#member);
         |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_return
         = note: `-W clippy::needless-return` implied by `-W clippy::all`
    help: remove `return`
         |
    2986 -             return quote!(#assign_to __default.#member);
    2986 +             quote!(#assign_to __default.#member)
         |

serde_derive/src/de.rs

@@ -2983,7 +2983,7 @@ fn expr_is_missing_seq(
     match *cattrs.default() {
         attr::Default::Default | attr::Default::Path(_) => {
             let member = &field.member;
-            return quote!(#assign_to __default.#member);
+            quote!(#assign_to __default.#member)
         }
         attr::Default::None => quote!(
             return _serde::__private::Err(_serde::de::Error::invalid_length(#index, &#expecting))