Fix bug in bytes_per_red option

Turns out this was never implemented correctly since it was referring to
the original bytes_per_iter atom.

c_src/jiffy.c

@@ -25,6 +25,7 @@ load(ErlNifEnv* env, void** priv, ERL_NIF_TERM info)
     st->atom_force_utf8 = make_atom(env, "force_utf8");
     st->atom_iter = make_atom(env, "iter");
     st->atom_bytes_per_iter = make_atom(env, "bytes_per_iter");
+    st->atom_bytes_per_red = make_atom(env, "bytes_per_red");
     st->atom_return_maps = make_atom(env, "return_maps");
     st->atom_return_trailer = make_atom(env, "return_trailer");
     st->atom_has_trailer = make_atom(env, "has_trailer");

c_src/jiffy.h

@@ -34,6 +34,7 @@ typedef struct {
     ERL_NIF_TERM    atom_force_utf8;
     ERL_NIF_TERM    atom_iter;
     ERL_NIF_TERM    atom_bytes_per_iter;
+    ERL_NIF_TERM    atom_bytes_per_red;
     ERL_NIF_TERM    atom_return_maps;
     ERL_NIF_TERM    atom_return_trailer;
     ERL_NIF_TERM    atom_has_trailer;

c_src/util.c

@@ -80,7 +80,7 @@ get_bytes_per_red(ErlNifEnv* env, ERL_NIF_TERM val, size_t* bpi)
         return 0;
     }
 
-    if(enif_compare(tuple[0], st->atom_bytes_per_iter) != 0) {
+    if(enif_compare(tuple[0], st->atom_bytes_per_red) != 0) {
         return 0;
     }