staging: comedi: ni_usb6501: remove useless check

Remove useless test in ni6501_send_command. The check is useless since this
function is called only in this driver.
Signed-off-by: Luca Ellero <luca.ellero@brickedbrain.com>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_usb6501.c

@@ -181,9 +181,6 @@ static int ni6501_send_command(struct comedi_device *dev, int command,
 	u8 *tx = devpriv->usb_tx_buf;
 	int ret;
 
-	if (!tx || !port)
-		return -EINVAL;
-
 	if (command != SET_PORT_DIR && !bitmap)
 		return -EINVAL;