staging: comedi: dyna_pci10xx: remove 'valid' from the private data

This variable is set at the end of the attach but never used
in the driver. Remove it.

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>