arm/sa1100: fix sa1100-rtc memory resource

DEFINE_RES_MEM() takes the size of resource as a second argument,
not the end address. Passing end address leads to following error
in runtime during device registration:
sa1100-rtc: failed to claim resource 0

Fix it.

Signed-off-by: Dmitry Artamonow <mad_soft@inbox.ru>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>