[ALSA] emu10k1 - Fix inverted Analog/Digital mixer switch on Audigy2

On Audigy2 Platinum, the Analog/Digital mixer switch is inverted.
	https://bugzilla.novell.com/show_bug.cgi?id=396204



The patch adds a simple workaround.

There might be another device requiring a similar fix, too (or fix for
audigy2 generically), but right now I fix only the known broken one.

Signed-off-by: Takashi Iwai <tiwai@suse.de>