usb: cdns3: fix static checker warning.

The patch c450e48eb570: "usb: cdns3: add power lost support for
system resume" from Feb 18, 2021, leads to the following static
checker warning:

        drivers/usb/cdns3/core.c:551 cdns_resume()
        error: uninitialized symbol 'ret'.

drivers/usb/cdns3/core.c
544
545     if (!role_changed) {
546            if (cdns->role == USB_ROLE_HOST)
547                  ret = cdns_drd_host_on(cdns);
548     else if (cdns->role == USB_ROLE_DEVICE)
549            ret = cdns_drd_gadget_on(cdns);

"ret" is uninitialized at else branch.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Frank Li <frank.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@kernel.org>