staging: comedi: adv_pci_dio: checkpatch.pl cleanup (missing blank line)

Fix this checkpatch.pl warning:

WARNING: Missing a blank line after declarations
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>

drivers/staging/comedi/drivers/adv_pci_dio.c

@@ -616,6 +616,7 @@ static int pci1760_mbxrequest(struct comedi_device *dev,
 	}
 	if (inb(dev->iobase + IMB2) == omb[2]) {
 		int retval;
+
 		retval = pci1760_clear_imb2(dev);
 		if (retval < 0)
 			return retval;