drivers/rtc/rtc-at91rm9200.c: make IO endian agnostic

Change the __raw IO calls to readl/write_relaxed which makes the driver
endian agnostic to run properly on big endian systems.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Andrew Victor <linux@maxim.org.za>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>