[media] s3c-camif: Fail on insufficient number of allocated buffers

Ensure the driver gets always at least its minimum required
number of buffers allocated by checking actual number of
allocated buffers in vb2_reqbufs(). And free any partially
allocated buffer queue with signaling an error to user space.
Without this patch applications may wait forever to dequeue
a filled buffer, because the hardware didn't even start after
VIDIOC_STREAMON, VIDIOC_QBUF calls, due to insufficient number
of empty buffers.

Reported-by: Alexander Nestorov <alexandernst@gmail.com>
Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/platform/s3c-camif/camif-capture.c

@@ -934,12 +934,19 @@ static int s3c_camif_reqbufs(struct file *file, void *priv,
 		vp->owner = NULL;
 
 	ret = vb2_reqbufs(&vp->vb_queue, rb);
-	if (!ret) {
-		vp->reqbufs_count = rb->count;
-		if (vp->owner == NULL && rb->count > 0)
-			vp->owner = priv;
+	if (ret < 0)
+		return ret;
+
+	if (rb->count && rb->count < CAMIF_REQ_BUFS_MIN) {
+		rb->count = 0;
+		vb2_reqbufs(&vp->vb_queue, rb);
+		ret = -ENOMEM;
 	}
 
+	vp->reqbufs_count = rb->count;
+	if (vp->owner == NULL && rb->count > 0)
+		vp->owner = priv;
+
 	return ret;
 }