platform/surface: dtx: Fix poll function

The poll function should not return -ERESTARTSYS.

Furthermore, locking in this function is completely unnecessary. The
ddev->lock protects access to the main device and controller (ddev->dev
and ddev->ctrl), ensuring that both are and remain valid while being
accessed by clients. Both are, however, never accessed in the poll
function. The shutdown test (via atomic bit flags) be safely done
without locking, so drop locking here entirely.
Reported-by: kernel test robot <lkp@intel.com>
Fixes: 1d609992 ("platform/surface: Add DTX driver)
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20210513134437.2431022-1-luzmaximilian@gmail.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/surface/surface_dtx.c

@@ -527,20 +527,14 @@ static __poll_t surface_dtx_poll(struct file *file, struct poll_table_struct *pt
 	struct sdtx_client *client = file->private_data;
 	__poll_t events = 0;
 
-	if (down_read_killable(&client->ddev->lock))
-		return -ERESTARTSYS;
-
-	if (test_bit(SDTX_DEVICE_SHUTDOWN_BIT, &client->ddev->flags)) {
-		up_read(&client->ddev->lock);
+	if (test_bit(SDTX_DEVICE_SHUTDOWN_BIT, &client->ddev->flags))
 		return EPOLLHUP | EPOLLERR;
-	}
 
 	poll_wait(file, &client->ddev->waitq, pt);
 
 	if (!kfifo_is_empty(&client->buffer))
 		events |= EPOLLIN | EPOLLRDNORM;
 
-	up_read(&client->ddev->lock);
 	return events;
 }