Currently, devt_attr for the "dev" file is freed immediately on device
removal, but if the "dev" sysfs file is open when a device is removed,
sysfs will access its attribute structure for further access including
close resulting in jumping to garbled address.  Fix it by postponing
freeing devt_attr to device release time.

Note that devt_attr for class_device is already freed on release.

This bug is reported by Chris Rankin as bugzilla bug#8198.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Chris Rankin <rankincj@yahoo.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>