src/msg/async/Event: collect and ignore return value for read()

src/msg/async/Event: collect and ignore return value for read()

Problem:
ceph/src/msg/async/Event.cc:58:9: warning: ignoring return value of ‘ssize_t read(int, void*, size_t)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
58 | read(fd_or_id, &value, sizeof(value));
| ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

‘warn_unused_result’ needs to be suppressed

Solution:
Collect and ignore return value for read to suppress ‘warn_unused_result’

Fixes: No Tracker
Signed-off-by: Kamoltat (Junior) Sirivadhna <ksirivad@redhat.com>