hantro: Make sure we don't use post-processor on an encoder

Commit 986eee3a ("media: hantro: Prevent encoders from using
post-processing") fixed hantro_needs_postproc condition,
but missed one case. Encoders don't have any post-processor
hardware block, so also can't be disabled.

Fix it.

Fixes: 986eee3a

 ("media: hantro: Prevent encoders from using post-processing")
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>