ffi/c_str.rs: Fix method/function confusion
ffi/c_str.rs: Fix method/function confusion

Per https://github.com/rust-lang/rust/pull/44855#discussion_r144049179

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust