Fix a memory order issue with weakly ordered systems

Fix a memory order issue with weakly ordered systems

this adds a dummy atomic release operation to update_qp, which
should make sure that the new value of reader_idx is visible in
get_hold_current_qp, directly after incrementing the users count.

Fixes: #26875
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26964)