media: rockchip/vpu: Remove a useless test

vdev is guaranteed to be equal to vpu->vfd_enc thanks a test done a few
lines above. Remove this useless test.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>