scsi: core: doc. fixes to scsi_common.c

Clean up some comment typos and fix some errors in documentation.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>