ARM: at91: pm: of_node_put() after its usage

Put node after it has been used.

Fixes: 13f16017 ("ARM: at91: pm: Tie the USB clock mask to the pmc")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1596616610-15460-4-git-send-email-claudiu.beznea@microchip.com