staging: comedi: adv_pci1723: cleanup card reset

Only one 'reset' of the card is required in the attach. Remove the
one before setting up the subdevices and leave the one before
exiting the attach function.

The 'valid' variable in the private data is not needed. This variable
is used in the detach to determine if it's ok to call the 'reset'
function. Checking if dev->iobase is valid works just as well.

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