scsi: core: check for equality of result byte values

When evaluating a SCSI command's result using the field access macros,
check for equality of the fields and not if a specific bit is set.

This is a preparation patch, for reworking the results field in the
SCSI command.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>