sync_file_range doesn't call down into the filesystem directly at all.
It only kicks off writeback of pagecache pages and optionally waits
on the result.

Convert sync_file_range to use errseq_t based error tracking, under the
assumption that most users will prefer this behavior when errors occur.
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJeff Layton <jlayton@redhat.com>