LU-17043 enc: fix osd lookup cache for long encrypted names

LU-17043 enc: fix osd lookup cache for long encrypted names

Fix osd lookup cache to support files with long encrypted names.
Those encrypted names can be up to 256 bytes, not NUL terminated.

Fixes: 29f8eb2a67 ("LU-16405 osd: lookup cache")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ica2329c8a0990395307a14fe9bb9d43db3b364ed
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52016
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>