vfe-480 is copied from vfe-17x and has the same racy idle timeout bug as in
17x.

Fix the vfe_disable_output() logic to no longer be racy and to conform
to the 17x way of quiescing and then resetting the VFE.

Fixes: 4edc8eae ("media: camss: Add initial support for VFE hardware version Titan 480")
Cc: stable@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>