Bluetooth: hci_bcm: Streamline runtime PM code

This driver seeks to force the Bluetooth device on for the duration of
5 seconds when the Bluetooth device has woken the host and after a
complete packet has been received.  It does that by calling:

    pm_runtime_get();
    pm_runtime_mark_last_busy();
    pm_runtime_put_autosuspend();

The same can be achieved more succinctly with:

    pm_request_resume();

That's because after runtime resuming the device, rpm_resume() invokes
pm_runtime_mark_last_busy() followed by rpm_idle(), which will cause
the device to be suspended after expiration of the autosuspend_delay.

No functional change intended.

Cc: Frédéric Danis <frederic.danis.oss@gmail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>