bluetooth: hci_ibs: disable irqs when spinlock is acquired

Deadlock is observed while performing bluetooth stress and
stability tests. Since same lock is getting acquired from both irq
and non-irq context, irqs should be disable while acquiring
the spinlock always. Otherwise there is chance of deadlock
observing while performing stability tests

Change-Id: I6921e7ed70362e1cbdc3f90543e0c906bab8f385
Signed-off-by: Anantha Krishnan <ananthk@codeaurora.org>