Use provided uid/gid for setattr

When changing the uid/gid of a file via zfs_setattr() use the
Posix id passed in iattr->ia_uid/gid.  While the zfs_fuid_create()
code already had the fuid support disabled for Linux it was
returning the uid/gid from the credential.  With this change
the 'chown' command which relies on setxattr is now working
properly.

Also remove a little stray white space which was in front of
zfs_update_inode() call and the end of zfs_setattr().