usb: cdns3: fix missing assignment of ret before error check on ret

usb: cdns3: fix missing assignment of ret before error check on ret

Currently the check on a non-zero return code in ret is false because
ret has been initialized to zero.  I believe that ret should be assigned
to the return from the call to readl_poll_timeout_atomic before the
check on ret.  Since ret is being re-assinged the original initialization
of ret to zero can be removed.

Addresses-Coverity: ("'Constant' variable guards dead code")
Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20190902145035.18200-1-colin.king@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>