net: microchip: Make `lan743x_pm_suspend` function return right value

drivers/net/ethernet/microchip/lan743x_main.c: In function lan743x_pm_suspend:

`ret` is set but not used. In fact, `pci_prepare_to_sleep` function value should
be the right value of `lan743x_pm_suspend` function, therefore, fix it.

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>