usb: xhci-mtk: fix bandwidth release issue

This happens when @udev->reset_resume is set to true, when usb resume,
the flow as below:
- hub_resume
- usb_disable_interface
- usb_disable_endpoint
- usb_hcd_disable_endpoint
- xhci_endpoint_disable // it set @ep->hcpriv to NULL

Then when reset usb device, it will drop allocated endpoints,
the flow as below:
- usb_reset_and_verify_device
- usb_hcd_alloc_bandwidth
- xhci_mtk_drop_ep

but @ep->hcpriv is already set to NULL, the bandwidth will be not
released anymore.

Due to the added endponts are stored in hash table, we can drop the check
of @ep->hcpriv.

Fixes: 4ce186665e7c ("usb: xhci-mtk: Do not use xhci's virt_dev in drop_endpoint")
Cc: stable <[e-mail]>
Signed-off-by: Chunfeng Yun <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/xhci-mtk-sch.c

···
 	if (ret)
 		return ret;
 
-	if (ep->hcpriv)
-		drop_ep_quirk(hcd, udev, ep);
+	/* needn't check @ep->hcpriv, xhci_endpoint_disable set it NULL */
+	drop_ep_quirk(hcd, udev, ep);
 
 	return 0;
 }