firewire: Use only a wait queue and terminate poll and read on device removal.

Drop the event list semaphore and only use the wait queue and the list
to synchronize queue access.  Break out of a poll or read whenever
the device is disconnected.

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>