firewire: ohci: omit IntEvent.busReset check rom AT queueing

Since commit 82b662dc "flush AT contexts after bus reset for OHCI 1.2",
the driver takes care of any AT packets that were enqueued during a bus
reset phase.  The check from commit 76f73ca1 is therefore no longer
necessary and the MMIO read can be avoided.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>