usb: chipidea: debug: check before accessing ci_role

ci_role BUGs when the role is >= CI_ROLE_END.

Cc: stable@vger.kernel.org  #v3.10+
Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at>
Signed-off-by: Peter Chen <peter.chen@nxp.com>