net/usb/r8152: make sure the USB buffer is DMA-able

Allocate the required memory before calling usb_control_msg. And
the additional memory copy is necessary.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>