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Several error paths didn't log why an error was returned. Add this.

Also handle the corner case of "adapter is unconfigured AND the message
is from Unregistered to TV AND reply is non-zero" separately and return
EINVAL in that case, since it really is an invalid value and not an
unconfigured CEC device.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>