Bluetooth: hci_ibs: Vote on/off UART clocks in non atomic context.

As per the latest clock design, we should not vote for the clocks
in the atomic context.

CRs-fixed: 377905
Change-Id: I70f269d40f007326de7a6279bfd11c4e576d251b
Signed-off-by: Ram Mohan Korukonda <rkorukon@codeaurora.org>