ceph: increase i_release_count when clear I_COMPLETE flag

If some dentries were pruned or FILE_SHARED cap was revoked while
readdir is in progress. make sure ceph_readdir() does not mark the
directory as complete.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
fs: fix dentry_lru_prune()

dentry_lru_prune() should always call file system's d_prune callback.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>