sysfs: add sysfs_dirent->s_name

Add s_name to sysfs_dirent.  This is to further reduce dependency to
the associated dentry.  Name is copied for directories and symlinks
but not for attributes.

Where possible, name dereferences are converted to use sd->s_name.
sysfs_symlink->link_name and sysfs_get_name() are unused now and
removed.

This change allows symlink to be implemented using sysfs_dirent tree
proper, which is the last remaining dentry-dependent sysfs walk.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index fd4b6dc..8240b16 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -454,7 +454,7 @@
 		goto out_unlock;
 	}
 
-	sd = sysfs_new_dirent((void *)attr, mode, type);
+	sd = sysfs_new_dirent(attr->name, (void *)attr, mode, type);
 	if (!sd) {
 		error = -ENOMEM;
 		goto out_unlock;