Fix tests on Linux

Author: asomers

test/test_unistd.rs

@@ -206,7 +206,7 @@ fn test_lseek64() {
     tmp.write(CONTENTS).unwrap();
     let tmpfd = tmp.into_raw_fd();
 
-    lseek64(tmp.as_raw_fd(), 5, Whence::SeekSet).unwrap();
+    lseek64(tmpfd, 5, Whence::SeekSet).unwrap();
 
     let mut buf = [0u8; 7];
     ::read_exact(tmpfd, &mut buf);