mm: filemap: remove unnecessary iitialization of ret

The ret variable can be defined without assigning a value, as it is
assigned before use.

Link: https://lkml.kernel.org/r/20231205022954.101045-1-zeming@nfschina.comSigned-off-by: Li zeming <zeming@nfschina.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/filemap.c

@@ -1623,7 +1623,7 @@ EXPORT_SYMBOL_GPL(__folio_lock_killable);
 static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
 {
 	struct wait_queue_head *q = folio_waitqueue(folio);
-	int ret = 0;
+	int ret;
 
 	wait->folio = folio;
 	wait->bit_nr = PG_locked;