mailbox: arm_mhuv2: make remove callback return void

My build tests failed to catch that amba driver that would have needed
adaption in commit 3fd269e74f2f ("amba: Make the remove callback return
void"). Change the remove function to make the driver build again.

Reported-by: kernel test robot <[e-mail]>
Fixes: 3fd269e74f2f ("amba: Make the remove callback return void")
Signed-off-by: Uwe Kleine-König <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

drivers/mailbox/arm_mhuv2.c

···
 	return ret;
 }
 
-static int mhuv2_remove(struct amba_device *adev)
+static void mhuv2_remove(struct amba_device *adev)
 {
 	struct mhuv2 *mhu = amba_get_drvdata(adev);
 
 	if (mhu->frame == SENDER_FRAME)
 		writel_relaxed(0x0, &mhu->send->access_request);
-
-	return 0;
 }
 
 static struct amba_id mhuv2_ids[] = {