ffi: fix build error from manual merge

I merged 8736dbec manually and accidentally broken the build.
diff --git a/src/ffi.rs b/src/ffi.rs
index 0721871..96b1dd0 100644
--- a/src/ffi.rs
+++ b/src/ffi.rs
@@ -789,7 +789,7 @@
     reason: &mut *const u8, reason_len: &mut size_t,
 ) -> bool {
     match &conn.peer_error {
-        Some(conn_error) => unsafe {
+        Some(conn_err) => unsafe {
             *is_app = conn_err.is_app;
             *error_code = conn_err.error_code;
             *reason = conn_err.reason.as_ptr();