staging: comedi: usbdux: fix errno (EL2NSYNC) check

These should both be checking the -errno.

Reported by: coverity
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc drivers/staging/comedi/drivers/usbdux.c
Simple merge