GFS2: Don't use MAXQUOTAS value

MAXQUOTAS value defines maximum number of quota types VFS supports.
This isn't necessarily the number of types gfs2 supports and with
addition of project quotas these two numbers stop matching. So make gfs2
use its private definition.

CC: cluster-devel@redhat.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>