f2fs: avoid page allocation for truncating partial inline_data

When truncating cached inline_data, we don't need to allocate a new page
all the time. Instead, it must check its page cache only.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index b74e9852..3b62949 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -523,7 +523,7 @@
 		return 0;
 
 	if (cache_only) {
-		page = f2fs_grab_cache_page(mapping, index, false);
+		page = find_lock_page(mapping, index);
 		if (page && PageUptodate(page))
 			goto truncate_out;
 		f2fs_put_page(page, 1);