firewire: ohci: initialize multiChanMode bits after reset

OHCI 1.1 says:
| Since the value of this bit is undefined after reset in all IR
| contexts, software shall initialize this bit to zero in all contexts
| whether or not active to maintain the exclusive nature of this bit.

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