vxfs warning fixes

gcc-4.3:

fs/freevxfs/vxfs_lookup.c: In function 'vxfs_find_entry':
fs/freevxfs/vxfs_lookup.c:139: warning: cast from pointer to integer of different size
fs/freevxfs/vxfs_lookup.c: In function 'vxfs_readdir':
fs/freevxfs/vxfs_lookup.c:294: warning: cast from pointer to integer of different size

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/freevxfs/vxfs_dir.h

@@ -80,7 +80,7 @@ struct vxfs_direct {
  *	a d_name with size len.
  */
 #define VXFS_DIRPAD		4
-#define VXFS_NAMEMIN		((int)((struct vxfs_direct *)0)->d_name)
+#define VXFS_NAMEMIN		offsetof(struct vxfs_direct, d_name)
 #define VXFS_DIRROUND(len)	((VXFS_DIRPAD + (len) - 1) & ~(VXFS_DIRPAD -1))
 #define VXFS_DIRLEN(len)	(VXFS_DIRROUND(VXFS_NAMEMIN + (len)))