staging: comedi: addi_apci_1564: remove use of devpriv->b_OutputMemoryStatus

This member of the private data struct is only set at one location in the
entire driver, and then never even used for anything.  Let's just remove
its use.

Signed-off-by: Chase Southwood <chase.southwood@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>