ieee1394: add documentation entry to MAINTAINERS

Add the file pattern of drivers/ieee1394/init_ohci1394_dma.c's
documentation to the maintainers database.  init_ohci1394_dma.c is not
really part of the IEEE 1394 subsystem, but this maintainers contact
seems to be better than none at all.

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