scsi: update description of logging_level bits

Update the description of 'scsi_logging_level' from 8 4-bit nibbles to
the (pre-git) reality of 10 3-bit bitfields.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Kyle Fortin <kyle.fortin@oracle.com>
Reviewed-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>