drivers/net/usb/r8152: remove the unneeded variable "ret" in rtl8152_system_suspend

rtl8152_system_suspend defines the variable "ret", but it is not modified
after initialization. So just remove it.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>