USB: gadget: udc: fix wrong pointer passed to IS_ERR() and PTR_ERR()

IS_ERR() and PTR_ERR() use wrong pointer, it should be
udc->virt_addr, fix it.

Fixes: 1b9f35ad ("usb: gadget: udc: Add Synopsys UDC Platform driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20210330130159.1051979-1-yangyingliang@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>