staging: comedi (adv_pci1723): coding style, fix whitespace before quoted newline

Small fix in adv_pci1723.c for a "whitespace before quoted newline" warning
from checkpatch.pl

Signed-off-by: Matt Billenstein <matt@vazor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>