scsi: Assign cancel_io vector for scsi_disk_emulate_ops

scsi: Assign cancel_io vector for scsi_disk_emulate_ops

Some emulated disk operations (MODE SELECT, UNMAP, WRITE SAME)
can trigger asynchronous I/Os.  Provide the cancel_io callback
to ensure that AIOCBs are properly cleaned up.

Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
Cc: qemu-stable@nongnu.org
[Tweak commit message. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 33325a53f15ab5370e1917b2a11cadffc77c5a52)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>