Staging: comedi: simply read and write functions in adl_pci8164

There are several read and write functions in adl_pci8164 that are
essentially the same thing.  They were created with a cut and paste.
Change them to use a common function.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>