Fix wrong variable checked in DoCheckUser auth callback

In DoCheckUser, after calling auth->checkUserCb(usr) into rc, the
failure check on line 1063 compared ret instead of rc against
WSSHD_AUTH_FAILURE. Since ret is WOLFSSH_USERAUTH_SUCCESS at that
point, the condition was always false, causing callback failures to
fall through to the generic error branch with WOLFSSH_USERAUTH_FAILURE
instead of returning WOLFSSH_USERAUTH_INVALID_USER.

Author: LinuxJedi

apps/wolfsshd/auth.c

@@ -1060,7 +1060,7 @@ static int DoCheckUser(const char* usr, WOLFSSHD_AUTH* auth)
             wolfSSH_Log(WS_LOG_INFO, "[SSHD] User ok.");
             ret = WOLFSSH_USERAUTH_SUCCESS;
         }
-        else if (ret == WSSHD_AUTH_FAILURE) {
+        else if (rc == WSSHD_AUTH_FAILURE) {
             wolfSSH_Log(WS_LOG_INFO, "[SSHD] User %s doesn't exist.", usr);
             ret = WOLFSSH_USERAUTH_INVALID_USER;
         }