net: ethernet: ixp4xx: Use distinct local variable

Use "ndev" for the struct net_device and "dev" for the
struct device in probe() and remove(). Add the local
"dev" pointer for later use in refactoring.

Take this opportunity to fix inverse christmas tree
coding style.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>