Change piece_attacks_square() API

An extra argument let us simplify some code.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/movegen.cpp

@@ -539,7 +539,7 @@ bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
   }
 
   // Luckly we can handle all the other pieces in one go
-  return (   pos.piece_attacks_square(from, to)
+  return (   pos.piece_attacks_square(pos.piece_on(from), from, to)
           && pos.pl_move_is_legal(m, pinned)
           && !move_promotion(m));
 }