Bluetooth: Remove unnecessary smp_mb__after_atomic() barriers

The barriers are redundant because atomic_test_and_clear_bit() already
provides the required full ordering for the cases in question (that is,
when the bit is cleared).

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>