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 <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serdev/core.c

···
  */
 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);
 }