Add missing call to crypt_random_exit
We call crypt_random_init in init_crypto, but never call crypt_random_exit. This change just copies what the crypt_backend functions do, and calls crypt_random_exit in the descructor.
We call crypt_random_init in init_crypto, but never call crypt_random_exit. This change just copies what the crypt_backend functions do, and calls crypt_random_exit in the descructor.