librbd/cache/pwl: move write_image_cache_state() out of m_lock

librbd/cache/pwl: move write_image_cache_state() out of m_lock

periodic_stats() will get m_lock, then get owner_lock. It is opposite
to the lock getting order of SnapshotCreateRequest::handle_notify_quiesce().
move write_image_cache_state() out of m_lock scope. After calling
update_image_cache_state(), and m_lock auto released, then call
write_image_cache_state() to update state in osds.

Fixes: https://tracker.ceph.com/issues/56703
Signed-off-by: Yin Congmin <congmin.yin@intel.com>
(cherry picked from commit a0e2868d9473a9120c4c5d478f6a592859ce1aec)