f2fs: implement a lock-free stat_show

The stat_show is just to show the current status of f2fs.
So, we can remove all the there-in locks.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 11fd8be..4beedccc 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -704,11 +704,7 @@
 
 static inline block_t valid_user_blocks(struct f2fs_sb_info *sbi)
 {
-	block_t ret;
-	spin_lock(&sbi->stat_lock);
-	ret = sbi->total_valid_block_count;
-	spin_unlock(&sbi->stat_lock);
-	return ret;
+	return sbi->total_valid_block_count;
 }
 
 static inline unsigned long __bitmap_size(struct f2fs_sb_info *sbi, int flag)
@@ -804,11 +800,7 @@
 
 static inline unsigned int valid_node_count(struct f2fs_sb_info *sbi)
 {
-	unsigned int ret;
-	spin_lock(&sbi->stat_lock);
-	ret = sbi->total_valid_node_count;
-	spin_unlock(&sbi->stat_lock);
-	return ret;
+	return sbi->total_valid_node_count;
 }
 
 static inline void inc_valid_inode_count(struct f2fs_sb_info *sbi)
@@ -829,11 +821,7 @@
 
 static inline unsigned int valid_inode_count(struct f2fs_sb_info *sbi)
 {
-	unsigned int ret;
-	spin_lock(&sbi->stat_lock);
-	ret = sbi->total_valid_inode_count;
-	spin_unlock(&sbi->stat_lock);
-	return ret;
+	return sbi->total_valid_inode_count;
 }
 
 static inline void f2fs_put_page(struct page *page, int unlock)