[ALSA] snd-emu10k1: Attenuate output volume to reduce distortion

Modules: EMU10K1/EMU10K2 driver

                      on Audigy 2 ZS Notebook.

Set the master volume to about 6 or 8% in alsamixer. This will
attenuate the output enough for better sound quality.
Note: Only stereo enabled at present.
The distortion is caused by the output path after the DSP
adding 12dB gain to the output while still in digital mode,
resulting in wrap around distortion.

Signed-off-by: James Courtier-Dutton <James@superbug.co.uk>