eth: mtk_ppe: fix up after merge

I missed this in the barrage of GCC 12 warnings. Commit cf2df74e
("net: fix dev_fill_forward_path with pppoe + bridge") changed
the pointer into an array.

Fixes: d7e6f583 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")
Link: https://lore.kernel.org/r/20220520012555.2262461-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>