splice: always updated atime in direct splice

Andre Majorel <aym-xunil@teaser.fr> points out that if we only updated
the atime when we transfer some data, we deviate from the standard
of always updating the atime. So change splice to always call
file_accessed() even if splice_direct_to_actor() didn't transfer
any data.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>