staging: comedi: comedi_test: use unsigned int for waveform timing

Use `unsigned int` instead of `unsigned long` to hold the period of the
fake waveform generator and the current time within each waveform.  The
waveform period will be no more than `INT_MAX` and the current time
within the waveform (prior to the modulo operation to bring it actually
within the waveform period) will be no more than `INT_MAX + UINT_MAX /
1000`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>