[ALSA] ymfpci: fix swapped channels in SPDIF output

Modules: YMFPCI driver

The routing of the effect 2/3 channels to the digital output is the
opposite of the rear analog output (left/right swapped).

We make the order correct for the digital output (which will make the
analog rear have the channels swapped) to make AC3 output work.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>