Correct typo in src/librustc_mir/const_eval.rs
Correct typo in src/librustc_mir/const_eval.rs

Co-Authored-By: lqd <405ac176f431502a634467186e072427d4a05b57@gmail.com>
graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust