media: davinci: remove unnecessary NULL check

We verified that "vpif_obj.sd[i]" is non-NULL on the previous line so
no need to check here.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>