gfs2: Don't try to sync non-changes

Function need_sync is supposed to determine if a qd element needs to be
synced. If the "change" (qd_change) is zero, it does not need to be
synced because there's literally no change in the value. Before this
patch need_sync returned false if value < 0. That should be <= 0.
This patch changes the check to <=.

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