[media] pxa_camera: remove an unused structure pointer

As reported by smatch:

drivers/media/platform/pxa_camera.c: In function 'pxa_dma_start_channels':
drivers/media/platform/pxa_camera.c:457:21: warning: variable 'active' set but not used [-Wunused-but-set-variable]
  struct pxa_buffer *active;
                     ^~~~~~
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/pxa_camera.c

@@ -455,9 +455,6 @@ static void pxa_videobuf_set_actdma(struct pxa_camera_dev *pcdev,
 static void pxa_dma_start_channels(struct pxa_camera_dev *pcdev)
 {
 	int i;
-	struct pxa_buffer *active;
-
-	active = pcdev->active;
 
 	for (i = 0; i < pcdev->channels; i++) {
 		dev_dbg(pcdev_to_dev(pcdev),