depmod: fix modules.builtin.alias.bin output

Due to wrong documentation on kmod_module_get_info() we ended up
checking for 0 as return. Check for > 0 to decided if we want to write
the index to the file, otherwise we would output a 0-sized index on
success.

tools/depmod.c

@@ -2457,7 +2457,7 @@ static int output_builtin_alias_bin(struct depmod *depmod, FILE *out)
 
 out:
 	/* do not bother writing the index if we are going to discard it */
-	if (!ret)
+	if (ret > 0)
 		index_write(idx, out);
 
 	if (builtin)