cec: Reset system audio mode status carefully [2/2]

PD#OTT-40245
BUG=266766058

Problem:
When there is a transmission error with <GIVE SYSTEM
AUDIO MODE STATUS> caused by cec busyness, playback
could reset the audio mode status and does not send
volume keyevents to the audio system then.

Solution:
Reset system audio mode status only with error NACK,
which means the target device is not connected.

Verify:
Walmart

Test: presubmits

Change-Id: Ife26b2251f40ee11cdbc86fe0797d29a74fb9be5
Signed-off-by: an.xi <an.xi@amlogic.com>