small cleanups

closes https://github.com/official-stockfish/Stockfish/pull/2695

No functional change

src/bitboard.h

@@ -253,7 +253,7 @@ inline Bitboard pawn_attack_span(Color c, Square s) {
 /// the given color and on the given square is a passed pawn.
 
 inline Bitboard passed_pawn_span(Color c, Square s) {
-  return forward_ranks_bb(c, s) & (adjacent_files_bb(s) | file_bb(s));
+  return pawn_attack_span(c, s) | forward_file_bb(c, s);
 }