net: netcp: fix cleanup interface list in netcp_remove()

Currently if user do rmmod keystone_netcp.ko following warning is
seen :-

[   59.035891] ------------[ cut here ]------------
[   59.040535] WARNING: CPU: 2 PID: 1619 at drivers/net/ethernet/ti/
netcp_core.c:2127 netcp_remove)

This is because the interface list is not cleaned up in netcp_remove.
This patch fixes this. Also fix some checkpatch related warnings.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>