ohci1394: clean up asynchronous and physical request filters programming

Various cleanups of how ohci1394 programs AsynchronousRequestFilter,
PhysicalRequestFilter, and physUpperBoundOffset. In particular, do not
rewrite registers within the bus reset interrupt handler if bus resets
do not affect the registers in the first place.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@modernduck.com>