media: venus: Warn only once about problems in .remove()

The only effect of returning an error code in a remove callback is that
the driver core emits a warning. The device is unbound anyhow.

As the remove callback already emits a (quite verbose) warning when ret
is non-zero, return zero to suppress the additional warning.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>