res_pjsip_phoneprov_provider: fix compile breakage on AST_VECTOR

endpoint->inbound_auths was changed to a vector in 13 and I
committed the 12 patch instead of the 13 patch.

Tested-by: George Joseph



git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@425052 f38db490-d61c-443f-a65b-d21fe96a405b