dm crypt: fix memory leak in crypt_ctr_cipher_old()

Fix memory leak of cipher_api.

Fixes: 33d2f09fcb35 (dm crypt: introduce new format of cipher with "capi:" prefix)
Cc: stable@vger.kernel.org # 4.12+
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-crypt.c

@@ -2466,6 +2466,7 @@ static int crypt_ctr_cipher_old(struct dm_target *ti, char *cipher_in, char *key
 		kfree(cipher_api);
 		return ret;
 	}
+	kfree(cipher_api);
 
 	return 0;
 bad_mem: