sata_mv: release clock on ata_host_activate() failure

mv_platfrom_probe() forgets to call clk_disable() and clk_put() iff
ata_host_activate() fails...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>