commit 2ddee91a upstream.

MacBook Air 5,2 has the same problem as MacBook Pro 8,1 where the
built-in mic records only the right channel.  Apply the same
workaround as MBP8,1 to spread the mono channel via a Cirrus codec
vendor-specific COEF setup.
Reported-and-tested-by: Vasil Zlatanov <vasil.zlatanov@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>