staging: vt6656: sparse fixes ethtool_ioctl Use struct ifreq *

Replace useraddr with direct point to struct ifreq->ifr_data

sparse warnings
main_usb.c:1443:44: warning: cast removes address space of expression
main_usb.c:1454:37: warning: incorrect type in argument 2 (different address spaces)
main_usb.c:1454:37:    expected void const [noderef] <asn:1>*from
main_usb.c:1454:37:    got void *useraddr
main_usb.c:1462:34: warning: incorrect type in argument 1 (different address spaces)
main_usb.c:1462:34:    expected void [noderef] <asn:1>*to
main_usb.c:1462:34:    got void *useraddr

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>