auth:rectify a cmake compilation warning

rectify src/auth/cephx/CephxProtocol.cc 1 warning
with the variable 'ch' Used before initialized
auth/cephx/CephxProtocol.cc:595:57: warning: '*((void*)& ch +8)' may be used uninitialized in this function [-Wmaybe-uninitialized]
     msg.server_challenge_plus_one = ch.server_challenge + 1;
                                     ~~~~~~~~~~~~~~~~~~~~^~~

Signed-off-by: cuiming <[email protected]>

Author: cuiming_yewu

src/auth/cephx/CephxProtocol.cc

@@ -584,7 +584,7 @@ bool CephXAuthorizer::add_challenge(CephContext *cct,
   auto p = challenge.begin();
   if (!p.end()) {
     std::string error;
-    CephXAuthorizeChallenge ch;
+    CephXAuthorizeChallenge ch{};
     decode_decrypt_enc_bl(cct, ch, session_key, challenge, error);
     if (!error.empty()) {
       ldout(cct, 0) << "failed to decrypt challenge (" << challenge.length() << " bytes): "