ARM: at91/pm: MOR register KEY was missing

Because writing the MOR register requires the PASSWD(0x37),
if missed, the write operation will be aborted.

Signed-off-by: Patrice Vilchez <patrice.vilchez@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>