staging: comedi: dmm32at: introduce dmm32at_reset()

For aesthetics, factor the board reset and detection code out of the
(*attach) function.

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