usb: chipidea: core: check before accessing ci_role in ci_role_show

ci_role BUGs when the role is >= CI_ROLE_END.
This is the case while the role is changing.

Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at>
Signed-off-by: Peter Chen <peter.chen@nxp.com>