In .probe(), devm_kzalloc() is called with size == 0 and works only
by luck, due to internal behavior of the allocator and the fact
that the proper allocation size is small. Let's use proper value for
calculating the size.

Fixes: cd6438c5 ("iommu/rockchip: Reconstruct to support multi slaves")
Signed-off-by: Shunqian Zheng <zhengsq@rock-chips.com>
Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>