of: Use NULL for pointers

Commit 4485681939b9 (of/fdt: Clean up casting in unflattening path)
modified unflatten_dt_node() to take a void * for the mem parameter
instead of an unsigned long. One of the call sites wasn't updated.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Grant Likely <grant.likely@linaro.org>

Conflicts:
	drivers/of/fdt.c
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: d2d3d7cd81e90e1ffac1a6eed7b3edcbf11f4c97
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>