LU-19113 llite: cfs_delete_from_page_cache() keep page locked

LU-19113 llite: cfs_delete_from_page_cache() keep page locked

Like in other places where generic_error_remove_folio() is
also being called, in both Lustre and Kernel, page should not
be unlocked prior to call it in cfs_delete_from_page_cache().

This was also allowing a race where page->mapping may become
NULL.

Taking an extra reference is also useless if page not unlocked
anymore.

Fixes: 738e69d4b9 ("LU-16292 llite: delete_from_page_cache not exported")
Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
Change-Id: If39575f4339afe460b3b1c955201e8f9cdfeb871
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59829
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>