Fix a clang warning in proxy_async.c where an unsigned value was being
unnecessarily compared against 0:
```
/home/kefu/dev/ceph/src/libcephfs_proxy/proxy_async.c:29:12: warning: result of comparison of unsigned expression >= 0 is always true [-Wtautological-unsigned-zero-compare]
29 | if ((size >= 0) && !info->write) {
| ~~~~ ^ ~
1 warning generated.
```
Since unsigned values are always >= 0 by definition, remove this
tautological check to resolve the "-Wtautological-unsigned-zero-compare"
warning.
Signed-off-by: Kefu Chai <tchaikov@gmail.com>
info->result = cbk->ll_nonblocking_rw.res;
- if ((size >= 0) && !info->write) {
+ if (!info->write) {
iov = info->iov;
count = info->iovcnt;
while (size > 0) {