doxygen: add newline after \file

While \file doesn't need an argument, it can't have another doxy
command after it.

intern/atomic/atomic_ops.h

@@ -44,7 +44,8 @@
  * The Original Code is: adapted from jemalloc.
  */
 
-/** \file \ingroup Atomic
+/** \file
+ * \ingroup Atomic
  *
  * \brief Provides wrapper around system-specific atomic primitives,
  * and some extensions (faked-atomic operations over float numbers).