V4L/DVB: media/mem2mem: dereferencing free memory

We dereferenced "ctx" on the error path.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/mem2mem_testdev.c

@@ -871,8 +871,10 @@ static int m2mtest_open(struct file *file)
 
 	ctx->m2m_ctx = v4l2_m2m_ctx_init(ctx, dev->m2m_dev, queue_init);
 	if (IS_ERR(ctx->m2m_ctx)) {
+		int ret = PTR_ERR(ctx->m2m_ctx);
+
 		kfree(ctx);
-		return PTR_ERR(ctx->m2m_ctx);
+		return ret;
 	}
 
 	atomic_inc(&dev->num_inst);