staging: unisys: visornic: remove useless memset

alloc_etherdev() calls alloc_netdev_mqs(), which
already uses kzalloc/vzalloc.

This clears a sparse warning :
drivers/staging/unisys/visornic/visornic_main.c:1366:15: warning: memset with byte count of 1460112

Signed-off-by: Hugo Camboulive <hugo.camboulive@gmail.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>