Fix bad assignment found by Flexelint

src/tus_file.c

@@ -269,7 +269,7 @@ tus_file_final_fini(struct tus_file_core *fcore)
 	assert(fcore->ptr_type == TFCP_CONCAT);
 	CAST_OBJ_NOTNULL(concat, fcore->ptr, TUS_CONCAT_MAGIC);
 	fcore->ptr = NULL;
-	fcore->ptr_type == TFCP_INVALID;
+	fcore->ptr_type = TFCP_INVALID;
 	assert (fcore->len >= sizeof *concat);
 	fcore->len = 0;