comment fixes in midlayer header files

Adjust tabulators, line wraps, empty lines, and comment style.
Update comments in ieee1394_transactions.h and highlevel.h.
Fix typo in comment in csr.h.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Ben Collins <bcollins@ubuntu.com>
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