gdth_exit would first remove all cards then stop the timer
and would not sync with the timer function. This caused a crash
in gdth_timer() when module was unloaded.
So del_timer_sync the timer before we delete the cards.

also the reboot notifier function would crash. So clean
that up and fix the crashes.
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>
Tested-by: NJoerg Dorchain: <joerg@dorchain.net>
Tested-by: NStefan Priebe <s.priebe@allied-internet.ag>
Tested-by: NJon Chelton <jchelton@ffpglobal.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>