staging: comedi: addi_apci_3xxx: remove 'b_AiInitialisation' from private data

This variable is set during the attach of the board and never cleared
so the test in i_APCI3XXX_InsnReadAnalogInput() will always succeed.
Just remove the variable to help with cleaning up this driver.

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>