net: cdc_ncm: remove redundant endpoint pointers

No need to duplicate stuff already in the common usbnet
struct.  We still need to keep our special find_endpoints
function because we need explicit control over the selected
altsetting.

Cc: Alexey Orishko <alexey.orishko@gmail.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>