Fix `deprecated` attribute for `__error`

src/unix/bsd/freebsdlike/dragonfly/errno.rs

 // DragonFlyBSD's __error function is declared with "static inline", so it must
 // be implemented in the libc crate, as a pointer to a static thread_local.
 f! {
-    #[deprecated(since = "0.2.77", "Use `__errno_location()` instead")]
+    #[deprecated(since = "0.2.77", note = "Use `__errno_location()` instead")]
     pub fn __error() -> *mut ::c_int {
         &mut errno
     }