Input: maplemouse - remove unused mdev->driver assignment

The driver field in struct maple_device is no longer used since
commit 1795cf48b322 ("sh/maple: clean maple bus code") which removed
the reading of this field.

Remove the unused assignment to mdev->driver and the now unused
mdrv variable in probe_maple_mouse.

Assisted-by: Antigravity:gemini-3.5-flash
Link: https://patch.msgid.link/20260703-b4-maple-cleanup-v1-11-41e424964da5@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/maplemouse.c

diff --git a/drivers/input/mouse/maplemouse.c b/drivers/input/mouse/maplemouse.c
index 37f60bb..f67e3eb 100644
--- a/drivers/input/mouse/maplemouse.c
+++ b/drivers/input/mouse/maplemouse.c
@@ -67,7 +67,6 @@ static void dc_mouse_close(struct input_dev *dev)
 static int probe_maple_mouse(struct device *dev)
 {
 	struct maple_device *mdev = to_maple_dev(dev);
-	struct maple_driver *mdrv = to_maple_driver(dev->driver);
 	int error;
 	struct input_dev *input_dev;
 	struct dc_mouse *mse;
@@ -102,9 +101,6 @@ static int probe_maple_mouse(struct device *dev)
 	error =	input_register_device(input_dev);
 	if (error)
 		goto fail_register;
-
-	mdev->driver = mdrv;
-
 	return error;
 
 fail_register: