ALSA: usb - Add boot quirk for C-Media 6206 USB Audio

Added boot quirk for C-Media CM6206 device in snd_usb_audio_probe.
The function snd_usb_cm6206_boot_quirk sets up six internal 16-bit
registers in order to initialize the device. Values for the registers
came from sniffing USB traffic under Windows since only four of the six
are documented in the datasheet for CM106 and some reserved bits were
also being set.

[Minor coding-style fixes by tiwai]

Signed-off-by: Dan Allongo <gongo2k1@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>