scsi-bus: Fix transfer length for VERIFY with BYTCHK=11b

The transfer length depends on field BYTCHK, which is encoded in byte
1, bits 1..2.  However, the guard for for case BYTCHK=11b doesn't
work, and we get case 01b instead.  Fix it.

Note that since emulated scsi-hd fails the command outright, it takes
SCSI passthrough of a device that actually implements VERIFY with
BYTCHK=11b to make the bug bite.

Screwed up in commit d12ad44.  Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>