* cipher/cipher-internal.h (cipher_block_add): New.
* cipher/blowfish.c (_gcry_blowfish_ctr_enc): Use new helper function
for CTR block increment.
* cipher/camellia-glue.c (_gcry_camellia_ctr_enc): Ditto.
* cipher/cast5.c (_gcry_cast5_ctr_enc): Ditto.
* cipher/cipher-ctr.c (_gcry_cipher_ctr_encrypt): Ditto.
* cipher/des.c (_gcry_3des_ctr_enc): Ditto.
* cipher/rijndael.c (_gcry_aes_ctr_enc): Ditto.
* cipher/serpent.c (_gcry_serpent_ctr_enc): Ditto.
* cipher/twofish.c (_gcry_twofish_ctr_enc): Ditto.