net: mediatek: check device_reset return code

The device_reset() function may fail, so we have to check
its return value, e.g. to make deferred probing work correctly.
gcc warns about it because of the warn_unused_result attribute:

drivers/net/ethernet/mediatek/mtk_eth_soc.c: In function 'mtk_probe':
drivers/net/ethernet/mediatek/mtk_eth_soc.c:1679:2: error: ignoring return value of 'device_reset', declared with attribute warn_unused_result [-Werror=unused-result]

This adds the trivial error check to propagate the return value
to the generic platform device probe code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>