udf: Convert descriptor index definitions to enum

Convert index definitions from defines to enum. It is a shorter
description and easier to modify. Also remove VDS_POS_VOL_DESC_PTR since
it is unused.
Acked-by: NPali Rohár <pali.rohar@gmail.com>
Signed-off-by: NJan Kara <jack@suse.cz>

fs/udf/super.c

@@ -64,14 +64,15 @@
 #include <linux/init.h>
 #include <linux/uaccess.h>
 
-#define VDS_POS_PRIMARY_VOL_DESC	0
-#define VDS_POS_UNALLOC_SPACE_DESC	1
-#define VDS_POS_LOGICAL_VOL_DESC	2
-#define VDS_POS_PARTITION_DESC		3
-#define VDS_POS_IMP_USE_VOL_DESC	4
-#define VDS_POS_VOL_DESC_PTR		5
-#define VDS_POS_TERMINATING_DESC	6
-#define VDS_POS_LENGTH			7
+enum {
+	VDS_POS_PRIMARY_VOL_DESC,
+	VDS_POS_UNALLOC_SPACE_DESC,
+	VDS_POS_LOGICAL_VOL_DESC,
+	VDS_POS_PARTITION_DESC,
+	VDS_POS_IMP_USE_VOL_DESC,
+	VDS_POS_TERMINATING_DESC,
+	VDS_POS_LENGTH
+};
 
 #define VSD_FIRST_SECTOR_OFFSET		32768
 #define VSD_MAX_SECTOR_OFFSET		0x800000