ocfs2: Consolidate validation of group descriptors.

Currently the validation of group descriptors is directly duplicated so
that one version can error the filesystem and the other (resize) can
just report the problem.  Consolidate to one function that takes a
boolean.  Wrap that function with the old call for the old users.

This is in preparation for lifting the read+validate step into a
single function.

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