Fixed EAP-TTLS server to verify eap_ttls_phase2_eap_init() return code

Fixed EAP-TTLS server to verify eap_ttls_phase2_eap_init() return code

It is possible that the initialization of the Phase 2 EAP method fails and
if that happens, we need to stop EAP-TTLS server from trying to continue
using the uninitialized EAP method. Otherwise, the server could trigger
a segmentation fault when dereferencing a NULL pointer.