f2fs: clean up the do_submit_bio flow

This patch introduces PAGE_TYPE_OF_BIO() and cleans up do_submit_bio() with it.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c73e3df..38963b4 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -350,6 +350,7 @@
  *			with waiting the bio's completion
  * ...			Only can be used with META.
  */
+#define PAGE_TYPE_OF_BIO(type)	((type) > META ? META : (type))
 enum page_type {
 	DATA,
 	NODE,