orinoco_usb: remove redundant pointer dev

The pointer dev is assigned but never read, hence it is redundant
and can be removed. Cleans up clang warning:

drivers/net/wireless/intersil/orinoco/orinoco_usb.c:1468:2: warning:
Value stored to 'dev' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>