fuse: mark pages accessed when written to

As fuse does not use the page cache library functions when userspace
writes to a file, it did not benefit from 'c8236db9 mm: mark page
accessed before we write_end()' that made sure pages are properly
marked accessed when written to.

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>