Staging: Comedi adv_pci1710: Combined two conditions

Combined two if statements making the code cleaner, removing one level
of indentation.

Signed-off-by: Tomas Melin <tomas.melin@iki.fi>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>