scsi: initialise info object with appropriate size

While processing controller 'CTRL_GET_INFO' command, the routine
'megasas_ctrl_get_info' overflows the '&info' object size. Use its
appropriate size to null initialise it.
Reported-by: NQinghao Tang <luodalongde@gmail.com>
Signed-off-by: NPrasad J Pandit <pjp@fedoraproject.org>
Message-Id: <alpine.LFD.2.20.1512211501420.22471@wniryva>
Cc: qemu-stable@nongnu.org
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NP J P <ppandit@redhat.com>

hw/scsi/megasas.c

@@ -718,7 +718,7 @@ static int megasas_ctrl_get_info(MegasasState *s, MegasasCmd *cmd)
     BusChild *kid;
     int num_pd_disks = 0;
 
-    memset(&info, 0x0, cmd->iov_size);
+    memset(&info, 0x0, dcmd_size);
     if (cmd->iov_size < dcmd_size) {
         trace_megasas_dcmd_invalid_xfer_len(cmd->index, cmd->iov_size,
                                             dcmd_size);