V4L/DVB: video/et61x251: improve error handling

The original code doesn't handle the situation where the controller is
not found.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/et61x251/et61x251_core.c

@@ -1713,7 +1713,7 @@ et61x251_vidioc_s_ctrl(struct et61x251_device* cam, void __user * arg)
 	if (copy_from_user(&ctrl, arg, sizeof(ctrl)))
 		return -EFAULT;
 
-	for (i = 0; i < ARRAY_SIZE(s->qctrl); i++)
+	for (i = 0; i < ARRAY_SIZE(s->qctrl); i++) {
 		if (ctrl.id == s->qctrl[i].id) {
 			if (s->qctrl[i].flags & V4L2_CTRL_FLAG_DISABLED)
 				return -EINVAL;
@@ -1723,7 +1723,9 @@ et61x251_vidioc_s_ctrl(struct et61x251_device* cam, void __user * arg)
 			ctrl.value -= ctrl.value % s->qctrl[i].step;
 			break;
 		}
-
+	}
+	if (i == ARRAY_SIZE(s->qctrl))
+		return -EINVAL;
 	if ((err = s->set_ctrl(cam, &ctrl)))
 		return err;