qos hook: fix spelling

Former code did not allow netting QoS peak value. Thanks Sven Kieske for
reporting this.

Change-Id: I39b7dfc512312ede8f4bc20fcef11310aa78730e
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20495
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>