Fix below NULL pointer dereference. we set ci->roles[CI_ROLE_GADGET]
too early in ci_hdrc_gadget_init(), if udc_start() fails due to some
reason, the ci->roles[CI_ROLE_GADGET] check in ci_hdrc_gadget_destroy
can't protect us.
We fix this issue by only setting ci->roles[CI_ROLE_GADGET] if
udc_start() succeed.