[Bluetooth] Eliminate checks for impossible conditions in IRQ handler

Our info structure and info->hdev is always passed to the IRQ handler,
so we don't have to worry about these checks in every interrupt.

Leave a BUG_ON() just to help unwary programmers, but these could
probably be removed as well.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>