common: remove spaces before literal operator

common: remove spaces before literal operator

clang 20 complains when compiling a user-defined literal operator
with spaces before the underscore. so let's drop the space to be
compliant to
[CWG2521](https://cplusplus.github.io/CWG/issues/2521.html).

```
/home/kefu/dev/ceph/src/common/options.h:415:41: warning: identifier '_min' preceded by whitespace in a literal operator declaration is deprecated [-Wdeprecated-literal-operator]
  415 | constexpr unsigned long long operator"" _min (unsigned long long min) {
      |                              ~~~~~~~~~~~^~~~
      |                              operator""_min
```

Signed-off-by: Kefu Chai <tchaikov@gmail.com>