staging: comedi: amplc_pc236_common: Use 16-bit 0 for interrupt data

The Amplicon PC36AT/PCI236 common driver has an "interrupt" subdevice
that supports Comedi asynchronous commands, placing a value in the
Comedi buffer for each interrupt.  The subdevice uses Comedi's 16-bit
sample format but the interrupt handler is calling
`comedi_buf_write_samples()` with the address of a 32-bit integer
`&s->state`.  On bigendian machines, this will copy 2 bytes from the
wrong end of the 32-bit integer.  This isn't really a problem since
`s->state` will always be 0 for this subdevice, but clean it up by using
a 16-bit variable initialized to 0 to pass the value.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210223143055.257402-11-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>