ARM: dts: Fix NAS4220B pin config

The DTS file for the NAS4220B had the pin config for the
ethernet interface set to the pins in the SL3512 SoC while
this system is using SL3516. Fix it by referencing the
right SL3516 pins instead of the SL3512 pins.

Cc: stable@vger.kernel.org
Cc: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Reported-by: Andreas Fiedler <andreas.fiedler@gmx.net>
Reported-by: Roman Yeryomin <roman@advem.lv>
Tested-by: Roman Yeryomin <roman@advem.lv>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>