f2fs: introduce get_dirty_dents for readability

The get_dirty_dents gives us the number of dirty dentry pages.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 292cc3c..59fac1a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -704,6 +704,11 @@
 	return atomic_read(&sbi->nr_pages[count_type]);
 }
 
+static inline int get_dirty_dents(struct inode *inode)
+{
+	return atomic_read(&F2FS_I(inode)->dirty_dents);
+}
+
 static inline int get_blocktype_secs(struct f2fs_sb_info *sbi, int block_type)
 {
 	unsigned int pages_per_sec = sbi->segs_per_sec *