scsi: virtio_scsi: fix handling of kmalloc failure

There is no check about the return value of kmalloc in
virtscsi_rescan_hotunplug. Add the check to avoid use
of null pointer 'inq_result' in case of the failure
of kmalloc.

Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
Message-Id: <20230202064124.22277-1-zyytlz.wz@163.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>