cifs: remove the kmap size limit from wsize

Now that we're not kmapping so much at once, there's no need to cap
the wsize at the amount that can be simultaneously kmapped.

Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>