libceph: stop parsing when a bad int arg is detected

There is no reason to continue option parsing after detecting
bad option.

[ Return match_int() errors from ceph_parse_options() to match the
  behaviour of parse_rbd_opts_token() and parse_fsopt_token(). ]

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>