staging: comedi: amplc_pc236: don't disable h/w interrupt on detach()

If an asynchronous command was running when the device is being
detached, the comedi core would have called the subdevice `cancel`
handler (`pc236_intr_cancel()`) before calling the `detach` handler
(`pc236_detach()`).  Since the cancel handler disables hardware
interrupts (at least for the PCI236 board) by calling
`pc236_disable_intr()`, there is no need for the detach handler to do so
as well.  Remove the call to `pc236_disable_intr()` from
`pc236_detach()`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>