b53: fix memory out of bounds access on 64 bit targets

On device reset the sizes for the vlan and port tables were wrongly
calculated based on the pointer size instead of the struct size. This
causes buffer overruns on 64 bit targets, resulting in panics.

Fix this by dereferencing the pointers.

Reported-by: Fedor Konstantinov <blmink@mink.su>
Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45938 3c298f89-4303-0410-b956-a3cf2f4a3e73