http: do not assign intermediate variable

No need for binding, it's only used in the next line to declare more
variables :)

PR-URL: https://github.com/nodejs/node/pull/17335


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>