usb: gadget: tegra-xudc: Fix crash in vbus_draw

Commit ac82b56b ("usb: gadget: tegra-xudc: Add vbus_draw support")
populated the vbus_draw callback for the Tegra XUDC driver. The function
tegra_xudc_gadget_vbus_draw(), that was added by this commit, assumes
that the pointer 'curr_usbphy' has been initialised, which is not always
the case because this is only initialised when the USB role is updated.
Fix this crash, by checking that the 'curr_usbphy' is valid before
dereferencing.

Fixes: ac82b56b ("usb: gadget: tegra-xudc: Add vbus_draw support")
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20230405181854.42355-1-jonathanh@nvidia.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/tegra-xudc.c

@@ -2167,7 +2167,7 @@ static int tegra_xudc_gadget_vbus_draw(struct usb_gadget *gadget,
 
 	dev_dbg(xudc->dev, "%s: %u mA\n", __func__, m_a);
 
-	if (xudc->curr_usbphy->chg_type == SDP_TYPE)
+	if (xudc->curr_usbphy && xudc->curr_usbphy->chg_type == SDP_TYPE)
 		ret = usb_phy_set_power(xudc->curr_usbphy, m_a);
 
 	return ret;