MFC	r251677:

Relax some unnecessary unsigned type changes in ext2fs.

While the changes in r245820 are in line with the ext2 spec,
the code derived from UFS can use negative values so it is
better to relax some types to keep them as they were, and
somewhat more similar to UFS. While here clean some casts.


git-svn-id: svn://svn.freebsd.org/base/stable/9@251798 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Merge remote-tracking branch 'upstream/svn_stable_9' into svn_stable_9