ocfs2: Pull ocfs2_xattr_value_buf up from __ocfs2_remove_xattr_range().

Place an ocfs2_xattr_value_buf in __ocfs2_xattr_shrink_size() and pass
it down to __ocfs2_remove_xattr_range().

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>