Bluetooth: hci_qca: Request Tx clock vote off only when Tx is pending

Tx pending flag is set to true when HOST IBS state is AWAKE or
AWAKEING. If IBS state is ASLEEP, then Tx clock is already voted
off. To optimize further directly calling serial_clock_vote()
instead of qca_wq_serial_tx_clock_vote_off(), at this point of
qca_suspend() already data is sent out. No need to wake up hci to
send data.

Signed-off-by: Balakrishna Godavarthi <bgodavar@codeaurora.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>