f2fs: introduce f2fs_flush_merged_bios for cleanup

Add a new helper f2fs_flush_merged_bios to clean up redundant codes.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 684c1e6..e43ab17 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1907,6 +1907,7 @@
 void f2fs_submit_merged_bio(struct f2fs_sb_info *, enum page_type, int);
 void f2fs_submit_merged_bio_cond(struct f2fs_sb_info *, struct inode *,
 				struct page *, nid_t, enum page_type, int);
+void f2fs_flush_merged_bios(struct f2fs_sb_info *);
 int f2fs_submit_page_bio(struct f2fs_io_info *);
 void f2fs_submit_page_mbio(struct f2fs_io_info *);
 void set_data_blkaddr(struct dnode_of_data *);