Fix device id data ptr using 0 instead of NULL

In some of the kernel modules, 0 is used instead of NULL to indicate
that there is no data in the of_device_id struct. These instances have
now been replaced with NULL instead.

Change-Id: I14f4aabf266bb5144107e101006e257bb7876782
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>