drivers/rtc/rtc-cmos.c: fix broken NVRAM bank 2 writing

Fix writing to NVRAM bank 2 in rtc-cmos driver.  It never worked since its
introduction in 2.6.28 because of a typo.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>