fjes: fix missed check in fjes_acpi_add

fjes_acpi_add() misses a check for platform_device_register_simple().
Add a check to fix it.

Fixes: 658d439b ("fjes: Introduce FUJITSU Extended Socket Network Device driver")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>