lib/rsa: don't use NULL as key_id

If keydir is not provided but name is we want to use name as key_id.

But with the current coding name is only used on its own if it is NULL
and keydir is provided which never occurs.

Fixes: 824ee745fb ("lib/rsa: Use the 'keyfile' argument from mkimage")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

lib/rsa/rsa-sign.c

@@ -269,7 +269,7 @@ static int rsa_engine_get_priv_key(const char *keydir, const char *name,
 			snprintf(key_id, sizeof(key_id),
 				 "%s%s",
 				 keydir, name);
-		else if (keydir)
+		else if (name)
 			snprintf(key_id, sizeof(key_id),
 				 "%s",
 				 name);