staging: comedi: dt2814: Don't wait for conversion in interrupt handler

When the interrupt handler decides the final sample has been acquired,
it turns off the timer enable (ENB) bit in the Command register.  That
triggers another A/D conversion.  The interrupt handler currently waits
for that to finish and then reads the resulting, unwanted sample.  Since
the functions for handling Comedi read instructions and for setting up
asynchronous commands now call `dt2814_ai_clear()` to wait for and
discard any spurious A/D conversion, let's remove that code from the
interrupt handler.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210301165757.243065-3-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>