firewire: ohci: log dead DMA contexts

When a DMA context goes into the dead state (and the controller thus
stops working correctly), logging this error and the controller's error
code might be helpful for debugging.

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