usb: renesas_usbhs: gadget: fix NULL pointer dereference in ep_disable()

commit 11432050 upstream.

This patch fixes an issue that the NULL pointer dereference happens
when we uses g_audio driver. Since the g_audio driver will call
usb_ep_disable() in afunc_set_alt() before it calls usb_ep_enable(),
the uep->pipe of renesas usbhs driver will be NULL. So, this patch
adds a condition to avoid the oops.
Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Fixes: 2f98382d (usb: renesas_usbhs: Add Renesas USBHS Gadget)
Signed-off-by: Felipe Balbi <balbi@ti.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/renesas_usbhs/mod_gadget.c

@@ -514,6 +514,10 @@ static int usbhsg_ep_enable(struct usb_ep *ep,
 static int usbhsg_ep_disable(struct usb_ep *ep)
 {
 	struct usbhsg_uep *uep = usbhsg_ep_to_uep(ep);
+	struct usbhs_pipe *pipe = usbhsg_uep_to_pipe(uep);
+
+	if (!pipe)
+		return -EINVAL;
 
 	return usbhsg_pipe_disable(uep);
 }