gfs2: Don't loop forever in gfs2_freeze if withdrawn

Before this patch, function gfs2_freeze would loop forever if the
filesystem it tries to freeze is withdrawn. That's because function
gfs2_lock_fs_check_clean tries to enqueue the glock of the journal and
the gfs2_glock returns -EIO because you can't enqueue a journaled glock
after a withdraw.

Move the check for file system withdraw inside the loop so that the loop
can end when withdraw occurs.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>