[SCSI] zfcp: Add docbook comments to debug trace.

Add missing docbook-comments for functions forming zfcp's internal
trace API.

Signed-off-by: Martin Peschke <mp3@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>