Driver Core: fix bug in device_rename() for SYSFS_DEPRECATED=y

This should fix the sysfs warnings that renaming network devices is
causing to show up with CONFIG_SYSFS_DEPRECATED=y

The code just shouldn't run if class devices are real directories, it's
an update for the symlink in the class directory. Nobody noticed that as
long as the creation of sysfs files silently failed, and we both missed
it before the merge, because we don't run SYSFS_DEPRECATED=y.        

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: David Miller <davem@davemloft.net>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>