[media] media: davinci: vpif_capture: use vb2_ops_wait_prepare/finish helper

This patch adds support in the capture driver for using
vb2_ops_wait_prepare/finish()  helpers provided by the
vb2 core.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>