fix error in MPIN example for one pass
fix error in MPIN example for one pass

milagro-crypto/milagro-crypto-c,miracl/milagro-crypto-c,miracl/milagro-crypto-c,miracl/milagro-crypto-c,philipp-cliqz/milagro-crypto-c,milagro-crypto/milagro-crypto-c,milagro-crypto/milagro-crypto-c,miracl/milagro-crypto-c,philipp-cliqz/milagro-crypto-c,milagro-crypto/milagro-crypto-c,philipp-cliqz/milagro-crypto-c,philipp-cliqz/milagro-crypto-c,miracl/milagro-crypto-c