media: imx: Remove incorrect check for queue state in start/stop_streaming

It is possible to call STREAMON without the minimum number of
buffers queued. In this case the vb2_queue state will be set to
streaming but the start_streaming vb2_op will not be called.
Later when enough buffers are queued, start_streaming will
be called but vb2_is_streaming will already return true.

Also removed the queue state check in stop_streaming since it's
not valid there either.

Signed-off-by: Ian Jamison <ian.dev@arkver.com>
Reviewed-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>