tty: serdev: core: Remove unused variable 'dummy'

No need to have a dummy variable here.

Fixes the following W=1 kernel build warning(s):

 drivers/tty/serdev/core.c: In function ‘serdev_controller_remove’:
 drivers/tty/serdev/core.c:791:6: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]

Cc: Rob Herring <robh@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104193549.4026187-2-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serdev/core.c

@@ -788,13 +788,10 @@ static int serdev_remove_device(struct device *dev, void *data)
  */
 void serdev_controller_remove(struct serdev_controller *ctrl)
 {
-	int dummy;
-
 	if (!ctrl)
 		return;
 
-	dummy = device_for_each_child(&ctrl->dev, NULL,
-				      serdev_remove_device);
+	device_for_each_child(&ctrl->dev, NULL, serdev_remove_device);
 	pm_runtime_disable(&ctrl->dev);
 	device_del(&ctrl->dev);
 }