usb: renesas_usbhs: gadget: fix giveback status code in usbhsg_pipe_disable()

A udc driver should set the giveback status to -ESHUTDOWN in
usb_ep_disable(). Otherwise, a gadget driver (e.g. g_serial) might
request next data wrongly and it is possible to cause kernel panic.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>