ext4: use errseq_t based error handling for reporting data writeback errors

Add a call to filemap_report_wb_err at the end of ext4_sync_file. This
will ensure that we check and advance the errseq_t in the file, which
allows us to track and report errors on all open fds when they occur.

Signed-off-by: Jeff Layton <jlayton@redhat.com>