[SCSI] boot options: correct option name and tell where to find docs for it

Minor corrections and additions to 'scsi_logging_level', as pointed out
by Chuck Ebbert.
Also point out the IBM S390-tools 'scsi_logging_level' script.
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

Documentation/kernel-parameters.txt

@@ -1593,7 +1593,13 @@ and is between 256 and 4096 characters. It is defined in the file
 			Format: <vendor>:<model>:<flags>
 			(flags are integer value)
 
-	scsi_logging=	[SCSI]
+	scsi_logging_level=	[SCSI] a bit mask of logging levels
+			See drivers/scsi/scsi_logging.h for bits.  Also
+			settable via sysctl at dev.scsi.logging_level
+			(/proc/sys/dev/scsi/logging_level).
+			There is also a nice 'scsi_logging_level' script in the
+			S390-tools package, available for download at
+			http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
 
 	scsi_mod.scan=	[SCSI] sync (default) scans SCSI busses as they are
 			discovered.  async scans them in kernel threads,