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: 824ee745fbca ("lib/rsa: Use the 'keyfile' argument from mkimage")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
index 085dc89..0e0a890 100644
--- a/lib/rsa/rsa-sign.c
+++ b/lib/rsa/rsa-sign.c
@@ -269,7 +269,7 @@
 			snprintf(key_id, sizeof(key_id),
 				 "%s%s",
 				 keydir, name);
-		else if (keydir)
+		else if (name)
 			snprintf(key_id, sizeof(key_id),
 				 "%s",
 				 name);