bluetooth: bluesleep: Exit early if device not registered

If the device isn't registered for this board, return out of the init
function early.

Reviewed-on: http://git-master/r/24254
Reviewed-by: Daniel Willemsen <dwillemsen@nvidia.com>
Tested-by: Daniel Willemsen <dwillemsen@nvidia.com>
Reviewed-by: Anantha Idapalapati <aidapalapati@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>

Change-Id: Ic806b4be1671a77a8fedc1c0376362bc177b0604