media: cec-pin: fix broken tx_ignore_nack_until_eom error injection

If the tx_ignore_nack_until_eom error injection was activated,
then tx_nacked was never set instead of setting it when the last
byte of the message was transmitted.

As a result the transmit was marked as OK, when it should have
been NACKed.

Modify the condition so that it always sets tx_nacked when the
last byte of the message was transmitted.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v4.17 and up
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>