net: e1000: remove repeated word "slot" for e1000_main.c

There are double "slot" in comment, so remove the redundant one.

Signed-off-by: Hao Chen <chenhao288@hisilicon.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>