Fix platform-specific doc string for AtomicUsize::from_mut to be platform-independent

Author: hkBst

core/src/sync/atomic.rs

@@ -2547,7 +2547,7 @@ macro_rules! atomic_int {
                 $int_type,
                 no = [
                     "**Note:** This function is only available on targets where `",
-                    stringify!($int_type), "` has an alignment of ", $align, " bytes."
+                    stringify!($atomic_type), "` has the same alignment as `", stringify!($int_type), "`."
                 ],
             }]
             ///