libceph: fix some spelling mistakes

Fix some spelling mistakes in comments:

- enconding ==> encoding
- ambigous ==> ambiguous
- orignal ==> original
- encyption ==> encryption

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>