net: hso: remove redundant unused variable dev

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

drivers/net/usb/hso.c:2280:2: warning: Value stored to 'dev' is
never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>