Bluetooth: Avoid a case where sleep is getting called in soft irq context

While turning off BT, sleep is getting called in the soft isr context
from work queue which is queued from a code section guarded under the
bh lock,
To resolve this released the bh lock before queing the work, as it wont
impact any BT functionality.

CRs-fixed: 405917
Change-Id: I1b872d724b4d0d384cc5314e0f493facd9829a54
Signed-off-by: Bhasker Neti <bneti@codeaurora.org>
Signed-off-by: Mallikarjuna GB <gbmalli@codeaurora.org>