Bluetooth: hci_qca: Only remove TX clock vote after TX is completed

qca_suspend() removes the vote for the UART TX clock after
writing an IBS sleep request to the serial buffer. This is
not a good idea since there is no guarantee that the request
has been sent at this point. Instead remove the vote after
successfully entering IBS sleep. This also fixes the issue
of the vote being removed in case of an aborted suspend due
to a failure of entering IBS sleep.

Fixes: 41d5b25f ("Bluetooth: hci_qca: add PM support")
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>