Split fe_set_b32 into reducing and normalizing variants

src/ecdsa_impl.h

@@ -239,7 +239,8 @@ static int secp256k1_ecdsa_sig_verify(const secp256k1_scalar *sigr, const secp25
 }
 #else
     secp256k1_scalar_get_b32(c, sigr);
-    secp256k1_fe_set_b32(&xr, c);
+    /* we can ignore the fe_set_b32_limit return value, because we know the input is in range */
+    (void)secp256k1_fe_set_b32_limit(&xr, c);
 
     /** We now have the recomputed R point in pr, and its claimed x coordinate (modulo n)
      *  in xr. Naively, we would extract the x coordinate from pr (requiring a inversion modulo p),