Staging: comedi: fix space before tabs coding style issue in adl_pci6208.c

This is a patch to the adl_pci6208.c file that fixes up a space before
tabs warning found by checkpatch.pl tool.
Signed-off-by: Jaakko Niemelä <mato@kyborgi.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>