[media] v4l2: vb2: fix queue reallocation and REQBUFS(0) case

This patch fixes 2 minor bugs in videobuf2 core:
1. Queue should be reallocated if one change the memory access
method without changing the number of buffers.
2. In case of REQBUFS(0), the request should not be passed to the
driver.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf2-core.c

@@ -488,7 +488,7 @@ int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 		return -EINVAL;
 	}
 
-	if (req->count == 0 || q->num_buffers != 0) {
+	if (req->count == 0 || q->num_buffers != 0 || q->memory != req->memory) {
 		/*
 		 * We already have buffers allocated, so first check if they
 		 * are not in use and can be freed.
@@ -501,6 +501,13 @@ int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 		ret = __vb2_queue_free(q);
 		if (ret != 0)
 			return ret;
+
+		/*
+		 * In case of REQBUFS(0) return immediately without calling
+		 * driver's queue_setup() callback and allocating resources.
+		 */
+		if (req->count == 0)
+			return 0;
 	}
 
 	/*