[media] media: davinci: vpif_display: fix the check on suspend/resume callbacks

It is possible to call STREAMON without having any buffers queued.
So vb2_is_streaming() can return true without start_streaming()
having been called. Only after at least one buffer has been
queued will start_streaming be called.

The check vb2_is_streaming() is incorrect as this would start
the DMA without having proper DMA pointers set up. this patch
uses vb2_start_streaming_called() instead to check is streaming
was called.

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>