Convert the mute LED handling in Sigmatel/IDT codec to the new vmaster
mute helper.  A point to be cautiously handled is that the value
passed to the callback is inverted; the vmaster passes "enabled"
(0 = mute), while LED classdev passes "brightness" (1 = mute).

A positive side-effect by this change is that the driver gets also the
enum controls for the mute behavior like other drivers already had.
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Link: https://lore.kernel.org/r/20200618110842.27238-12-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>