mfd: terminate pcf50633 i2c_device_id list

The i2c_device_id list is supposed to be zero-terminated.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Balaji Rao <balajirrao@openmoko.org>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>