Don't pass loginmsg by address now that it's an sshbuf*

In 120a1ec74, loginmsg was changed from the legacy Buffer type
to struct sshbuf*, but it missed changing calls to
sys_auth_allowed_user and sys_auth_record_login which passed
loginmsg by address. Now that it's a pointer, just pass it directly.

This only affects AIX, unless there are out of tree users.
diff --git a/auth.c b/auth.c
index 18d0857..d2a8cd6 100644
--- a/auth.c
+++ b/auth.c
@@ -258,7 +258,7 @@
 	}
 
 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
-	if (!sys_auth_allowed_user(pw, &loginmsg))
+	if (!sys_auth_allowed_user(pw, loginmsg))
 		return 0;
 #endif
 
@@ -362,7 +362,7 @@
 	if (authenticated)
 		sys_auth_record_login(authctxt->user,
 		    auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
-		    &loginmsg);
+		    loginmsg);
 # endif
 #endif
 #ifdef SSH_AUDIT_EVENTS