drivers/rtc/rtc-ab8500.c: Revoke Device Tree enablement

All AB8500 devices are now registered via MFD core, so Device Tree
capability is no longer required for probing. Here we pull the DT
match table to ensure we're no longer probed during Device Tree
start-up.

CC: Alessandro Zummo <a.zummo@towertech.it>
CC: rtc-linux@googlegroups.com
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>