io_uring: initialize 'timeout' properly in io_sq_thread()

Some static checker reports below warning:
    fs/io_uring.c:6939 io_sq_thread()
    error: uninitialized symbol 'timeout'.

This is a false positive, but let's just initialize 'timeout' to make
sure we don't trip over this.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -6908,7 +6908,7 @@ static int io_sq_thread(void *data)
 	const struct cred *old_cred = NULL;
 	struct io_sq_data *sqd = data;
 	struct io_ring_ctx *ctx;
-	unsigned long timeout;
+	unsigned long timeout = 0;
 	DEFINE_WAIT(wait);
 
 	task_lock(current);