ALSA: ice1712: Correcting/completing #defines for REGS

This small patch completes #defines for Control/Status Register,
adds comments for the missing ones there and on the Interrupt Mask
Register and additionally corrects "#define ICE1712_SERR_LEVEL 0x04 -> 0x08",
according to documentation.

Signed-off-by: Konstantinos Tsimpoukas <kostaslinuxxx@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>