staging: comedi: ni_usb6501: remove empty lines

ni6501_send_command(): remove empty lines in case statements

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>