usb: cdnsp: fix cdnsp_decode_trb function to properly handle ret value

Variable ret in function cdnsp_decode_trb is initialized but not
used. To fix this compiler warning patch adds checking whether the
data buffer has not been overflowed.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Link: https://lore.kernel.org/r/20220112053237.14309-1-pawell@gli-login.cadence.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>