ubifs: Drop softlimit and delta fields from struct ubifs_wbuf
Values of these fields are set during init and never modified. They are
used (read) in a single function only. There isn't really any reason to
keep them in a struct. It only makes struct just a bit bigger without
any visible gain.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl> Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com> Signed-off-by: Richard Weinberger <richard@nod.at>