udf: replace udf_*_offset macros with functions

- translate udf_file_entry_alloc_offset macro into function
- translate udf_ext0_offset macro into function
- add comment about crypticly named fields in struct udf_inode_info

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/udf_i.h b/fs/udf/udf_i.h
index d6d9a77..4f86b1d 100644
--- a/fs/udf/udf_i.h
+++ b/fs/udf/udf_i.h
@@ -12,8 +12,8 @@
 	__u32			i_next_alloc_block;
 	__u32			i_next_alloc_goal;
 	unsigned		i_alloc_type : 3;
-	unsigned		i_efe : 1;
-	unsigned		i_use : 1;
+	unsigned		i_efe : 1;	/* extendedFileEntry */
+	unsigned		i_use : 1;	/* unallocSpaceEntry */
 	unsigned		i_strat4096 : 1;
 	unsigned		reserved : 26;
 	union {