flist: add flist_first_entry()

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/trim.c b/trim.c
index de792dc..a7f1b86 100644
--- a/trim.c
+++ b/trim.c
@@ -24,7 +24,7 @@
 		return 1;
 
 	assert(td->trim_entries);
-	ipo = flist_entry(td->trim_list.next, struct io_piece, trim_list);
+	ipo = flist_first_entry(&td->trim_list, struct io_piece, trim_list);
 	remove_trim_entry(td, ipo);
 
 	io_u->offset = ipo->offset;