net-sysfs: Fix inconsistent of format with argument type in net-sysfs.c

Fix follow warnings:
[net/core/net-sysfs.c:1161]: (warning) %u in format string (no. 1)
	requires 'unsigned int' but the argument type is 'int'.
[net/core/net-sysfs.c:1162]: (warning) %u in format string (no. 1)
	requires 'unsigned int' but the argument type is 'int'.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>