sysfs: switch to ->s_d_op and ->d_release()

a) ->d_iput() is wrong here - what we do to inode is completely usual, it's
dentry->d_fsdata that we want to drop.  Just use ->d_release().

b) switch to ->s_d_op - no need to play with d_set_d_op()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 52c3bdb6..c15a7a3 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -68,6 +68,7 @@
 	}
 	root->d_fsdata = &sysfs_root;
 	sb->s_root = root;
+	sb->s_d_op = &sysfs_dentry_ops;
 	return 0;
 }