f2fs: use list_for_each_entry{_safe} for simplyfying code

This patch use list_for_each_entry{_safe} instead of list_for_each{_safe} for
simplfying code.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 570ab9a..cb49e639 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -340,8 +340,7 @@
 void clear_prefree_segments(struct f2fs_sb_info *sbi)
 {
 	struct list_head *head = &(SM_I(sbi)->discard_list);
-	struct list_head *this, *next;
-	struct discard_entry *entry;
+	struct discard_entry *entry, *this;
 	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
 	unsigned long *prefree_map = dirty_i->dirty_segmap[PRE];
 	unsigned int total_segs = TOTAL_SEGS(sbi);
@@ -370,8 +369,7 @@
 	mutex_unlock(&dirty_i->seglist_lock);
 
 	/* send small discards */
-	list_for_each_safe(this, next, head) {
-		entry = list_entry(this, struct discard_entry, list);
+	list_for_each_entry_safe(entry, this, head, list) {
 		f2fs_issue_discard(sbi, entry->blkaddr, entry->len);
 		list_del(&entry->list);
 		SM_I(sbi)->nr_discards -= entry->len;