staging: comedi: amplc_dio200: refactor dio200_handle_read_intr()

Refactor `dio200_handle_read_intr()` to fix checkpatch warning about too
many leading tabs.  Factor out the part that puts the scan data into the
asynchronous command data buffer and checks for end of acquisition into
new function `dio200_read_scan_intr()`.

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