Deduplicate info.used_crate_source indexing

Author: bjorn3

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -263,9 +263,10 @@ pub fn each_linked_rlib(
             None => return Err("could not find formats for rlibs".to_string()),
         }
         let name = &info.crate_name[&cnum];
-        let path = if let Some((path, _)) = &info.used_crate_source[&cnum].rlib {
+        let used_crate_source = &info.used_crate_source[&cnum];
+        let path = if let Some((path, _)) = &used_crate_source.rlib {
             path
-        } else if info.used_crate_source[&cnum].rmeta.is_some() {
+        } else if used_crate_source.rmeta.is_some() {
             return Err(format!(
                 "could not find rlib for: `{}`, found rmeta (metadata) file",
                 name