fuse warning fix

gcc-4.3:

fs/fuse/dir.c: In function 'parse_dirfile':
fs/fuse/dir.c:833: warning: cast from pointer to integer of different size
fs/fuse/dir.c:835: warning: cast from pointer to integer of different size

[miklos@szeredi.hu: use offsetof]
Acked-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fuse.h

@@ -339,7 +339,7 @@ struct fuse_dirent {
 	char name[0];
 };
 
-#define FUSE_NAME_OFFSET ((unsigned) ((struct fuse_dirent *) 0)->name)
+#define FUSE_NAME_OFFSET offsetof(struct fuse_dirent, name)
 #define FUSE_DIRENT_ALIGN(x) (((x) + sizeof(__u64) - 1) & ~(sizeof(__u64) - 1))
 #define FUSE_DIRENT_SIZE(d) \
 	FUSE_DIRENT_ALIGN(FUSE_NAME_OFFSET + (d)->namelen)