media: coda: clear error return value before picture run

The error return value is not written by some firmware codecs, such as
MPEG-2 decode on CodaHx4. Clear the error return value before starting
the picture run to avoid misinterpreting unrelated values returned by
sequence initialization as error return value.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>