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.

CRs-fixed: 406705
Change-Id: I4c79e3f7edb5312d02e6819fb62384f58c2e1d32
Signed-off-by: Ram Mohan Korukonda <rkorukon@codeaurora.org>