ARM: at91: pm: use proper master clock register offset

SAM9X60's PMC has different master clock register offset than the other
SoCs' PMC. Due to this, specify master clock register offset based
on PMC compatible and pass it to pm_suspend.S since it is also needed
in there. When PM part for SAM9X60 was published the SAM9X60's PMC
(commit f6deae46039c ("clk: at91: add sam9x60 pmc driver")) wasn't
integrated.

Fixes: 01c7031c ("ARM: at91: pm: initial PM support for SAM9X60")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1579522208-19523-2-git-send-email-claudiu.beznea@microchip.com