scsi: scsi_devinfo: fixup string compare

When checking the model and vendor string we need to use the minimum
value of either string, otherwise we'll miss out on wildcard matches.

And we should take care when matching with zero size strings; results
might be unpredictable.  With this patch the rules for matching devinfo
strings are as follows:

- Vendor strings must match exactly
- Empty Model strings will only match if the devinfo model
  is also empty
- Model strings shorter than the devinfo model string will
  not match

Fixes: 5e7ff2ca ("SCSI: fix new bug in scsi_dev_info_list string matching")
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>